C# Data Types

C# Data Types

As explained in the variables chapter, a variable in C# must be a specified data type:

int myNum = 5;               // Integer (whole number)
double myDoubleNum = 5.99D;  // Floating point number
char myLetter = 'D';         // Character
bool myBool = true;          // Boolean
string myText = "Hello";     // String

A data type specifies the size and type of variable values.

It is important to use the correct data type for the corresponding variable; to avoid errors, to save time and memory, but it will also make your code more maintainable and readable. The most common data types are:

Numbers

Number types are divided into two groups:

Integer types stores whole numbers, positive or negative (such as 123 or -456), without decimals. Valid types are int and long. Which type you should use, depends on the numeric value.

Floating point types represents numbers with a fractional part, containing one or more decimals. Valid types are float and double.

Integer Types

Int

The int data type can store whole numbers from -2147483648 to 2147483647. In general, and in our tutorial, the int data type is the preferred data type when we create variables with a numeric value.

int myNum = 100000;
Console.WriteLine(myNum);

Long

The long data type can store whole numbers from -9223372036854775808 to 9223372036854775807. This is used when int is not large enough to store the value. Note that you should end the value with an "L":

long myNum = 15000000000L;
Console.WriteLine(myNum);

Floating Point Types

You should use a floating point type whenever you need a number with a decimal, such as 9.99 or 3.14515.

The float and double data types can store fractional numbers. Note that you should end the value with an "F" for floats and "D" for doubles:

float myNum = 5.75F;
Console.WriteLine(myNum);

double myNum = 19.99D;
Console.WriteLine(myNum);

Scientific Numbers

A floating point number can also be a scientific number with an "e" to indicate the power of 10:

float f1 = 35e3F;
double d1 = 12E4D;
Console.WriteLine(f1);
Console.WriteLine(d1);

Booleans

A boolean data type is declared with the bool keyword and can only take the values true or false:

bool isCSharpFun = true;
bool isFishTasty = false;
Console.WriteLine(isCSharpFun);   // Outputs True
Console.WriteLine(isFishTasty);   // Outputs False

Boolean values are mostly used for conditional testing, which you will learn more about in a later chapter.

Characters

The char data type is used to store a single character. The character must be surrounded by single quotes, like 'A' or 'c':

char myGrade = 'B';
Console.WriteLine(myGrade);

Strings

The string data type is used to store a sequence of characters (text). String values must be surrounded by double quotes:

string greeting = "Hello World";
Console.WriteLine(greeting);

C# Type Casting

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C# Type Casting

Type casting is when you assign a value of one data type to another type.

In C#, there are two types of casting:

• Implicit Casting (automatically) - converting a smaller type to a larger type size
  char -> int -> long -> float -> double
  
  
• Explicit Casting (manually) - converting a larger type to a smaller size type
  double -> float -> long -> int -> char

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Implicit Casting

Implicit casting is done automatically when passing a smaller size type to a larger size type:

Example

int myInt = 9;
double myDouble = myInt;       // Automatic casting: int to double

Console.WriteLine(myInt);      // Outputs 9
Console.WriteLine(myDouble);   // Outputs 9

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Explicit Casting

Explicit casting must be done manually by placing the type in parentheses in front of the value:

Example

double myDouble = 9.78;
int myInt = (int) myDouble;    // Manual casting: double to int

Console.WriteLine(myDouble);   // Outputs 9.78
Console.WriteLine(myInt);      // Outputs 9

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Type Conversion Methods

It is also possible to convert data types explicitly by using built-in methods, such as Convert.ToBoolean, Convert.ToDouble, Convert.ToString, Convert.ToInt32 (int) and Convert.ToInt64 (long):

Example

int myInt = 10;
double myDouble = 5.25;
bool myBool = true;

Console.WriteLine(Convert.ToString(myInt));    // convert int to string
Console.WriteLine(Convert.ToDouble(myInt));    // convert int to double
Console.WriteLine(Convert.ToInt32(myDouble));  // convert double to int
Console.WriteLine(Convert.ToString(myBool));   // convert bool to string

Why Conversion?

Many times, there's no need for type conversion. But sometimes you have to. Take a look at the next chapter, when working with , to see an example of this.

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C# User Input

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Get User Input

You have already learned that Console.WriteLine() is used to output (print) values. Now we will use Console.ReadLine() to get user input.

In the following example, the user can input his or hers username, which is stored in the variable userName. Then we print the value of userName:

Example

// Type your username and press enter
Console.WriteLine("Enter username:");

// Create a string variable and get user input from the keyboard and store it in the variable
string userName = Console.ReadLine();

// Print the value of the variable (userName), which will display the input value
Console.WriteLine("Username is: " + userName);

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User Input and Numbers

The Console.ReadLine() method returns a string. Therefore, you cannot get information from another data type, such as int. The following program will cause an error:

Example

Console.WriteLine("Enter your age:");
int age = Console.ReadLine();
Console.WriteLine("Your age is: " + age);

The error message will be something like this:

Cannot implicitly convert type 'string' to 'int'

Like the error message says, you cannot implicitly convert type 'string' to 'int'.

Luckily, for you, you just learned from the , that you can convert any type explicitly, by using one of the Convert.To methods:

Example

Console.WriteLine("Enter your age:");
int age = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Your age is: " + age);

Note: If you enter wrong input (e.g. text in a numerical input), you will get an exception/error message (like System.FormatException: 'Input string was not in a correct format.').

You will learn more about and how to handle errors in a later chapter.

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C# Operators

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Operators

Operators are used to perform operations on variables and values.

In the example below, we use the + operator to add together two values:

Example

int x = 100 + 50;

Although the + operator is often used to add together two values, like in the example above, it can also be used to add together a variable and a value, or a variable and another variable:

Example

int sum1 = 100 + 50;        // 150 (100 + 50)
int sum2 = sum1 + 250;      // 400 (150 + 250)
int sum3 = sum2 + sum2;     // 800 (400 + 400)

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Arithmetic Operators

Arithmetic operators are used to perform common mathematical operations:

Operator	Name	Description	Example	Try it
+	Addition	Adds together two values	x + y
-	Subtraction	Subtracts one value from another	x - y
*	Multiplication	Multiplies two values	x * y
/	Division	Divides one value by another	x / y
%	Modulus	Returns the division remainder	x % y
++	Increment	Increases the value of a variable by 1	x++
--	Decrement	Decreases the value of a variable by 1	x--

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C# Operators

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Operators

Operators are used to perform operations on variables and values.

In the example below, we use the + operator to add together two values:

Example

int x = 100 + 50;

Although the + operator is often used to add together two values, like in the example above, it can also be used to add together a variable and a value, or a variable and another variable:

Example

int sum1 = 100 + 50;        // 150 (100 + 50)
int sum2 = sum1 + 250;      // 400 (150 + 250)
int sum3 = sum2 + sum2;     // 800 (400 + 400)

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Arithmetic Operators

Arithmetic operators are used to perform common mathematical operations:

Operator	Name	Description	Example	Try it
+	Addition	Adds together two values	x + y
-	Subtraction	Subtracts one value from another	x - y
*	Multiplication	Multiplies two values	x * y
/	Division	Divides one value by another	x / y
%	Modulus	Returns the division remainder	x % y
++	Increment	Increases the value of a variable by 1	x++
--	Decrement	Decreases the value of a variable by 1	x--

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C# Exercises

Test Yourself With Exercises

Exercise:

Multiply 10 with 5, and print the result.

Console.WriteLine(10  5);

Submit Answer »

C# Assignment Operators

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Assignment Operators

Assignment operators are used to assign values to variables.

In the example below, we use the assignment operator (=) to assign the value 10 to a variable called x:

Example

int x = 10;

The addition assignment operator (+=) adds a value to a variable:

Example

int x = 10;
x += 5;

A list of all assignment operators:

Operator	Example	Same As	Try it
=	x = 5	x = 5
+=	x += 3	x = x + 3
-=	x -= 3	x = x - 3
*=	x *= 3	x = x * 3
/=	x /= 3	x = x / 3
%=	x %= 3	x = x % 3
&=	x &= 3	x = x & 3
|=	x |= 3	x = x | 3
^=	x ^= 3	x = x ^ 3
>>=	x >>= 3	x = x >> 3
<<=	x <<= 3	x = x << 3

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C# Comparison Operators

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Comparison Operators

Comparison operators are used to compare two values (or variables). This is important in programming, because it helps us to find answers and make decisions.

The return value of a comparison is either True or False. These values are known as Boolean values, and you will learn more about them in the and chapter.

In the following example, we use the greater than operator (>) to find out if 5 is greater than 3:

Example

int x = 5;
int y = 3;
Console.WriteLine(x > y); // returns True because 5 is greater than 3

A list of all comparison operators:

Operator	Name	Example	Try it
==	Equal to	x == y
!=	Not equal	x != y
>	Greater than	x > y
<	Less than	x < y
>=	Greater than or equal to	x >= y
<=	Less than or equal to	x <= y

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C# Logical Operators

 

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Logical Operators

As with , you can also test for True or False values with logical operators.

Logical operators are used to determine the logic between variables or values:

Operator	Name	Description	Example	Try it
&&	Logical and	Returns True if both statements are true	x < 5 &&  x < 10
||	Logical or	Returns True if one of the statements is true	x < 5 || x < 4
!	Logical not	Reverse the result, returns False if the result is true	!(x < 5 && x < 10)

You will learn more about comparison and logical operators in the and chapters.

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C# Math

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The C# Math class has many methods that allows you to perform mathematical tasks on numbers.

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Math.Max(x,y)

The Math.Max(x,y) method can be used to find the highest value of x and y:

Example

Math.Max(5, 10);

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Math.Min(x,y)

The Math.Min(x,y) method can be used to find the lowest value of of x and y:

Example

Math.Min(5, 10);

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Math.Sqrt(x)

The Math.Sqrt(x) method returns the square root of x:

Example

Math.Sqrt(64);

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Math.Abs(x)

The Math.Abs(x) method returns the absolute (positive) value of x:

Example

Math.Abs(-4.7);

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Math.Round()

Math.Round() rounds a number to the nearest whole number:

Example

Math.Round(9.99);

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C# Strings

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C# Strings

Strings are used for storing text.

A string variable contains a collection of characters surrounded by double quotes:

Example

Create a variable of type string and assign it a value:

string greeting = "Hello";

A string variable can contain many words, if you want:

Example

string greeting2 = "Nice to meet you!";

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String Length

A string in C# is actually an object, which contain properties and methods that can perform certain operations on strings. For example, the length of a string can be found with the Length property:

Example

string txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
Console.WriteLine("The length of the txt string is: " + txt.Length);

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Other Methods

There are many string methods available, for example ToUpper() and ToLower(), which returns a copy of the string converted to uppercase or lowercase:

Example

string txt = "Hello World";
Console.WriteLine(txt.ToUpper());   // Outputs "HELLO WORLD"
Console.WriteLine(txt.ToLower());   // Outputs "hello world"

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C# Strings

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C# Strings

Strings are used for storing text.

A string variable contains a collection of characters surrounded by double quotes:

Example

Create a variable of type string and assign it a value:

string greeting = "Hello";

A string variable can contain many words, if you want:

Example

string greeting2 = "Nice to meet you!";

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String Length

A string in C# is actually an object, which contain properties and methods that can perform certain operations on strings. For example, the length of a string can be found with the Length property:

Example

string txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
Console.WriteLine("The length of the txt string is: " + txt.Length);

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Other Methods

There are many string methods available, for example ToUpper() and ToLower(), which returns a copy of the string converted to uppercase or lowercase:

Example

string txt = "Hello World";
Console.WriteLine(txt.ToUpper());   // Outputs "HELLO WORLD"
Console.WriteLine(txt.ToLower());   // Outputs "hello world"

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C# String Concatenation

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String Concatenation

The + operator can be used between strings to combine them. This is called concatenation:

Example

string firstName = "John ";
string lastName = "Doe";
string name = firstName + lastName;
Console.WriteLine(name);

Note that we have added a space after "John" to create a space between firstName and lastName on print.

You can also use the string.Concat() method to concatenate two strings:

Example

string firstName = "John ";
string lastName = "Doe";
string name = string.Concat(firstName, lastName);
Console.WriteLine(name);

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Adding Numbers and Strings

WARNING!

C# uses the + operator for both addition and concatenation.

Remember: Numbers are added. Strings are concatenated.

If you add two numbers, the result will be a number:

Example

int x = 10;
int y = 20;
int z = x + y;  // z will be 30 (an integer/number)

If you add two strings, the result will be a string concatenation:

Example

string x = "10";
string y = "20";
string z = x + y;  // z will be 1020 (a string)

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C# String Interpolation

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String Interpolation

Another option of , is string interpolation, which substitutes values of variables into placeholders in a string. Note that you do not have to worry about spaces, like with concatenation:

Example

string firstName = "John";
string lastName = "Doe";
string name = $"My full name is: {firstName} {lastName}";
Console.WriteLine(name);

Also note that you have to use the dollar sign ($) when using the string interpolation method.

String interpolation was introduced in C# version 6.

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C# Access Strings

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Access Strings

You can access the characters in a string by referring to its index number inside square brackets [].

This example prints the first character in myString:

Example

string myString = "Hello";
Console.WriteLine(myString[0]);  // Outputs "H"

Note: String indexes start with 0: [0] is the first character. [1] is the second character, etc.

This example prints the second character (1) in myString:

Example

string myString = "Hello";
Console.WriteLine(myString[1]);  // Outputs "e"

You can also find the index position of a specific character in a string, by using the IndexOf() method:

Example

string myString = "Hello";
Console.WriteLine(myString.IndexOf("e"));  // Outputs "1"

Another useful method is Substring(), which extracts the characters from a string, starting from the specified character position/index, and returns a new string. This method is often used together with IndexOf() to get the specific character position:

Example

// Full name
string name = "John Doe";

// Location of the letter D
int charPos = name.IndexOf("D");

// Get last name
string lastName = name.Substring(charPos);

// Print the result
Console.WriteLine(lastName);

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C# Special Characters

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Strings - Special Characters

Because strings must be written within quotes, C# will misunderstand this string, and generate an error:

string txt = "We are the so-called "Vikings" from the north.";

The solution to avoid this problem, is to use the backslash escape character.

The backslash () escape character turns special characters into string characters:

Escape character	Result	Description
'	'	Single quote
"	"	Double quote
\		Backslash

The sequence "  inserts a double quote in a string:

Example

string txt = "We are the so-called "Vikings" from the north.";

The sequence '  inserts a single quote in a string:

Example

string txt = "It's alright.";

The sequence \  inserts a single backslash in a string:

Example

string txt = "The character \ is called backslash.";

Other useful escape characters in C# are:

Code	Result	Try it
n	New Line
t	Tab
b	Backspace

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C# Exercises

Test Yourself With Exercises

Exercise:

Fill in the missing part to create a greeting variable of type string and assign it the value Hello.

  = ;

Submit Answer »

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C# Booleans

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C# Booleans

Very often, in programming, you will need a data type that can only have one of two values, like:

• YES / NO
• ON / OFF
• TRUE / FALSE

For this, C# has a bool data type, which can take the values true or false.

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Boolean Values

A boolean type is declared with the bool keyword and can only take the values true or false:

Example

bool isCSharpFun = true;
bool isFishTasty = false;
Console.WriteLine(isCSharpFun);   // Outputs True
Console.WriteLine(isFishTasty);   // Outputs False

However, it is more common to return boolean values from boolean expressions, for conditional testing (see below).

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Boolean Expression

A Boolean expression returns a boolean value: True or False, by comparing values/variables.

This is useful to build logic, and find answers.

For example, you can use a , such as the greater than (>) operator to find out if an expression (or a variable) is true:

Example

int x = 10;
int y = 9;
Console.WriteLine(x > y); // returns True, because 10 is higher than 9

Or even easier:

Example

Console.WriteLine(10 > 9); // returns True, because 10 is higher than 9

In the examples below, we use the equal to (==) operator to evaluate an expression:

Example

int x = 10;
Console.WriteLine(x == 10); // returns True, because the value of x is equal to 10

Example

Console.WriteLine(10 == 15); // returns False, because 10 is not equal to 15

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Real Life Example

Let's think of a "real life example" where we need to find out if a person is old enough to vote.

In the example below, we use the >= comparison operator to find out if the age (25) is greater than OR equal to the voting age limit, which is set to 18:

Example

int myAge = 25;
int votingAge = 18;
Console.WriteLine(myAge >= votingAge);

Cool, right? An even better approach (since we are on a roll now), would be to wrap the code above in an if...else statement, so we can perform different actions depending on the result:

Example

Output "Old enough to vote!" if myAge is greater than or equal to 18. Otherwise output "Not old enough to vote.":

int myAge = 25;
int votingAge = 18;

if (myAge >= votingAge) 
{
  Console.WriteLine("Old enough to vote!");
} 
else 
{
  Console.WriteLine("Not old enough to vote.");
}

The boolean value of an expression is the basis for all C# comparisons and conditions.

You will learn more about in the next chapter.

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C# If ... Else

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C# Conditions and If Statements

C# supports the usual logical conditions from mathematics:

• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Equal to a == b
• Not Equal to: a != b

You can use these conditions to perform different actions for different decisions.

C# has the following conditional statements:

• Use if to specify a block of code to be executed, if a specified condition is true
• Use else to specify a block of code to be executed, if the same condition is false
• Use else if to specify a new condition to test, if the first condition is false
• Use switch to specify many alternative blocks of code to be executed

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The if Statement

Use the if statement to specify a block of C# code to be executed if a condition is True.

Syntax

if (condition) 
{
  // block of code to be executed if the condition is True
}

Note that if is in lowercase letters. Uppercase letters (If or IF) will generate an error.

In the example below, we test two values to find out if 20 is greater than 18. If the condition is True, print some text:

Example

if (20 > 18) 
{
  Console.WriteLine("20 is greater than 18");
}

We can also test variables:

Example

int x = 20;
int y = 18;
if (x > y) 
{
  Console.WriteLine("x is greater than y");
}

Example explained

In the example above we use two variables, x and y, to test whether x is greater than y (using the > operator). As x is 20, and y is 18, and we know that 20 is greater than 18, we print to the screen that "x is greater than y".

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C# If ... Else

 

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C# Conditions and If Statements

C# supports the usual logical conditions from mathematics:

• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Equal to a == b
• Not Equal to: a != b

You can use these conditions to perform different actions for different decisions.

C# has the following conditional statements:

• Use if to specify a block of code to be executed, if a specified condition is true
• Use else to specify a block of code to be executed, if the same condition is false
• Use else if to specify a new condition to test, if the first condition is false
• Use switch to specify many alternative blocks of code to be executed

---

The if Statement

Use the if statement to specify a block of C# code to be executed if a condition is True.

Syntax

if (condition) 
{
  // block of code to be executed if the condition is True
}

Note that if is in lowercase letters. Uppercase letters (If or IF) will generate an error.

In the example below, we test two values to find out if 20 is greater than 18. If the condition is True, print some text:

Example

if (20 > 18) 
{
  Console.WriteLine("20 is greater than 18");
}

 

We can also test variables:

Example

int x = 20;
int y = 18;
if (x > y) 
{
  Console.WriteLine("x is greater than y");
}

 

Example explained

In the example above we use two variables, x and y, to test whether x is greater than y (using the > operator). As x is 20, and y is 18, and we know that 20 is greater than 18, we print to the screen that "x is greater than y".

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C# The else Statement

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The else Statement

Use the else statement to specify a block of code to be executed if the condition is False.

Syntax

if (condition)
{
  // block of code to be executed if the condition is True
} 
else 
{
  // block of code to be executed if the condition is False
}

Example

int time = 20;
if (time < 18) 
{
  Console.WriteLine("Good day.");
} 
else 
{
  Console.WriteLine("Good evening.");
}
// Outputs "Good evening."

Example explained

In the example above, time (20) is greater than 18, so the condition is False. Because of this, we move on to the else condition and print to the screen "Good evening". If the time was less than 18, the program would print "Good day".

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C# The else if Statement

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The else if Statement

Use the else if statement to specify a new condition if the first condition is False.

Syntax

if (condition1)
{
  // block of code to be executed if condition1 is True
} 
else if (condition2) 
{
  // block of code to be executed if the condition1 is false and condition2 is True
} 
else
{
  // block of code to be executed if the condition1 is false and condition2 is False
}

Example

int time = 22;
if (time < 10) 
{
  Console.WriteLine("Good morning.");
} 
else if (time < 20) 
{
  Console.WriteLine("Good day.");
} 
else 
{
  Console.WriteLine("Good evening.");
}
// Outputs "Good evening."

Example explained

In the example above, time (22) is greater than 10, so the first condition is False. The next condition, in the else if statement, is also False, so we move on to the else condition since condition1 and condition2 is both False - and print to the screen "Good evening".

However, if the time was 14, our program would print "Good day."

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C# Short Hand If...Else

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Short Hand If...Else (Ternary Operator)

There is also a short-hand if else, which is known as the ternary operator because it consists of three operands. It can be used to replace multiple lines of code with a single line. It is often used to replace simple if else statements:

Syntax

variable = (condition) ? expressionTrue :  expressionFalse;

Instead of writing:

Example

int time = 20;
if (time < 18) 
{
  Console.WriteLine("Good day.");
} 
else 
{
  Console.WriteLine("Good evening.");
}

You can simply write:

Example

int time = 20;
string result = (time < 18) ? "Good day." : "Good evening.";
Console.WriteLine(result);

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C# Exercises

Test Yourself With Exercises

Exercise:

Print "Hello World" if x is greater than y.

int x = 50;
int y = 10;
 (x  y) 
{
  Console.WriteLine("Hello World");
}

Submit Answer »

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C# Switch

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C# Switch Statements

Use the switch statement to select one of many code blocks to be executed.

Syntax

switch(expression) 
{
  case x:
    // code block
    break;
  case y:
    // code block
    break;
  default:
    // code block
    break;
}

This is how it works:

• The switch expression is evaluated once
• The value of the expression is compared with the values of each case
• If there is a match, the associated block of code is executed
• The break and default keywords will be described later in this chapter

The example below uses the weekday number to calculate the weekday name:

Example

int day = 4;
switch (day) 
{
  case 1:
    Console.WriteLine("Monday");
    break;
  case 2:
    Console.WriteLine("Tuesday");
    break;
  case 3:
    Console.WriteLine("Wednesday");
    break;
  case 4:
    Console.WriteLine("Thursday");
    break;
  case 5:
    Console.WriteLine("Friday");
    break;
  case 6:
    Console.WriteLine("Saturday");
    break;
  case 7:
    Console.WriteLine("Sunday");
    break;
}
// Outputs "Thursday" (day 4)

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The break Keyword

When C# reaches a break keyword, it breaks out of the switch block.

This will stop the execution of more code and case testing inside the block.

When a match is found, and the job is done, it's time for a break. There is no need for more testing.

A break can save a lot of execution time because it "ignores" the execution of all the rest of the code in the switch block.

---

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The default Keyword

The default keyword is optional and specifies some code to run if there is no case match:

Example

int day = 4;
switch (day) 
{
  case 6:
    Console.WriteLine("Today is Saturday.");
    break;
  case 7:
    Console.WriteLine("Today is Sunday.");
    break;
  default:
    Console.WriteLine("Looking forward to the Weekend.");
    break;
}
// Outputs "Looking forward to the Weekend."

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C# While Loop

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Loops

Loops can execute a block of code as long as a specified condition is reached.

Loops are handy because they save time, reduce errors, and they make code more readable.

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C# While Loop

The while loop loops through a block of code as long as a specified condition is True:

Syntax

while (condition) 
{
  // code block to be executed
}

In the example below, the code in the loop will run, over and over again, as long as a variable (i) is less than 5:

Example

int i = 0;
while (i < 5) 
{
  Console.WriteLine(i);
  i++;
}

Note: Do not forget to increase the variable used in the condition, otherwise the loop will never end!

---

The Do/While Loop

The do/while loop is a variant of the while loop. This loop will execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.

Syntax

do 
{
  // code block to be executed
}
while (condition);

The example below uses a do/while loop. The loop will always be executed at least once, even if the condition is false, because the code block is executed before the condition is tested:

Example

int i = 0;
do 
{
  Console.WriteLine(i);
  i++;
}
while (i < 5);

Do not forget to increase the variable used in the condition, otherwise the loop will never end!

---

C# For Loop

---

C# For Loop

When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop:

Syntax

for (statement 1; statement 2; statement 3) 
{
  // code block to be executed
}

Statement 1 is executed (one time) before the execution of the code block.

Statement 2 defines the condition for executing the code block.

Statement 3 is executed (every time) after the code block has been executed.

The example below will print the numbers 0 to 4:

Example

for (int i = 0; i < 5; i++) 
{
  Console.WriteLine(i);
}

Example explained

Statement 1 sets a variable before the loop starts (int i = 0).

Statement 2 defines the condition for the loop to run (i must be less than 5). If the condition is true, the loop will start over again, if it is false, the loop will end.

Statement 3 increases a value (i++) each time the code block in the loop has been executed.

---

Another Example

This example will only print even values between 0 and 10:

Example

for (int i = 0; i <= 10; i = i + 2) 
{
  Console.WriteLine(i);
}

---

Nested Loops

It is also possible to place a loop inside another loop. This is called a nested loop.

The "inner loop" will be executed one time for each iteration of the "outer loop":

Example

// Outer loop
for (int i = 1; i <= 2; ++i) 
{
  Console.WriteLine("Outer: " + i);  // Executes 2 times

  // Inner loop
  for (int j = 1; j <= 3; j++) 
  {
    Console.WriteLine(" Inner: " + j); // Executes 6 times (2 * 3)
  }
}

---

C# For Loop

---

C# For Loop

When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop:

Syntax

for (statement 1; statement 2; statement 3) 
{
  // code block to be executed
}

Statement 1 is executed (one time) before the execution of the code block.

Statement 2 defines the condition for executing the code block.

Statement 3 is executed (every time) after the code block has been executed.

The example below will print the numbers 0 to 4:

Example

for (int i = 0; i < 5; i++) 
{
  Console.WriteLine(i);
}

Example explained

Statement 1 sets a variable before the loop starts (int i = 0).

Statement 2 defines the condition for the loop to run (i must be less than 5). If the condition is true, the loop will start over again, if it is false, the loop will end.

Statement 3 increases a value (i++) each time the code block in the loop has been executed.

---

Another Example

This example will only print even values between 0 and 10:

Example

for (int i = 0; i <= 10; i = i + 2) 
{
  Console.WriteLine(i);
}

---

Nested Loops

It is also possible to place a loop inside another loop. This is called a nested loop.

The "inner loop" will be executed one time for each iteration of the "outer loop":

Example

// Outer loop
for (int i = 1; i <= 2; ++i) 
{
  Console.WriteLine("Outer: " + i);  // Executes 2 times

  // Inner loop
  for (int j = 1; j <= 3; j++) 
  {
    Console.WriteLine(" Inner: " + j); // Executes 6 times (2 * 3)
  }
}

---

C# Exercises

Test Yourself With Exercises

Exercise:

Use a for loop to print "Yes" 5 times:

 (int i = 0; i < 5; ) 
{
  Console.WriteLine("Yes");
}

Submit Answer »

---

C# Foreach Loop

---

The foreach Loop

There is also a foreach loop, which is used exclusively to loop through elements in an array:

Syntax

foreach (type variableName in arrayName) 
{
  // code block to be executed
}

The following example outputs all elements in the cars array, using a foreach loop:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
foreach (string i in cars) 
{
  Console.WriteLine(i);
}

Note: Don't worry if you don't understand the example above. You will learn more about Arrays in the .

---

C# Break and Continue

---

C# Break

You have already seen the break statement used in an earlier chapter of this tutorial. It was used to "jump out" of a switch statement.

The break statement can also be used to jump out of a loop.

This example jumps out of the loop when i is equal to 4:

Example

for (int i = 0; i < 10; i++) 
{
  if (i == 4) 
  {
    break;
  }
  Console.WriteLine(i);
}

---

C# Continue

The continue statement breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop.

This example skips the value of 4:

Example

for (int i = 0; i < 10; i++) 
{
  if (i == 4) 
  {
    continue;
  }
  Console.WriteLine(i);
}

---

Break and Continue in While Loop

You can also use break and continue in while loops:

Break Example

int i = 0;
while (i < 10) 
{
  Console.WriteLine(i);
  i++;
  if (i == 4) 
  {
    break;
  }
}

Continue Example

int i = 0;
while (i < 10) 
{
  if (i == 4) 
  {
    i++;
    continue;
  }
  Console.WriteLine(i);
  i++;
}

---

C# Arrays

---

Create an Array

Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.

To declare an array, define the variable type with square brackets:

string[] cars;

We have now declared a variable that holds an array of strings.

To insert values to it, we can use an array literal - place the values in a comma-separated list, inside curly braces:

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};

To create an array of integers, you could write:

int[] myNum = {10, 20, 30, 40};

---

Access the Elements of an Array

You access an array element by referring to the index number.

This statement accesses the value of the first element in cars:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Console.WriteLine(cars[0]);
// Outputs Volvo

Note: Array indexes start with 0: [0] is the first element. [1] is the second element, etc.

---

---

Change an Array Element

To change the value of a specific element, refer to the index number:

Example

cars[0] = "Opel";

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
cars[0] = "Opel";
Console.WriteLine(cars[0]);
// Now outputs Opel instead of Volvo

---

Array Length

To find out how many elements an array has, use the Length property:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Console.WriteLine(cars.Length);
// Outputs 4

---

Other Ways to Create an Array

If you are familiar with C#, you might have seen arrays created with the new keyword, and perhaps you have seen arrays with a specified size as well. In C#, there are different ways to create an array:

// Create an array of four elements, and add values later
string[] cars = new string[4];

// Create an array of four elements and add values right away 
string[] cars = new string[4] {"Volvo", "BMW", "Ford", "Mazda"};

// Create an array of four elements without specifying the size 
string[] cars = new string[] {"Volvo", "BMW", "Ford", "Mazda"};

// Create an array of four elements, omitting the new keyword, and without specifying the size
string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};

It is up to you which option you choose. In our tutorial, we will often use the last option, as it is faster and easier to read.

However, you should note that if you declare an array and initialize it later, you have to use the new keyword:

// Declare an array
string[] cars;

// Add values, using new
cars = new string[] {"Volvo", "BMW", "Ford"};

// Add values without using new (this will cause an error)
cars = {"Volvo", "BMW", "Ford"};

---

C# Arrays

---

Create an Array

Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.

To declare an array, define the variable type with square brackets:

string[] cars;

We have now declared a variable that holds an array of strings.

To insert values to it, we can use an array literal - place the values in a comma-separated list, inside curly braces:

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};

To create an array of integers, you could write:

int[] myNum = {10, 20, 30, 40};

---

Access the Elements of an Array

You access an array element by referring to the index number.

This statement accesses the value of the first element in cars:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Console.WriteLine(cars[0]);
// Outputs Volvo

Note: Array indexes start with 0: [0] is the first element. [1] is the second element, etc.

---

---

Change an Array Element

To change the value of a specific element, refer to the index number:

Example

cars[0] = "Opel";

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
cars[0] = "Opel";
Console.WriteLine(cars[0]);
// Now outputs Opel instead of Volvo

---

Array Length

To find out how many elements an array has, use the Length property:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Console.WriteLine(cars.Length);
// Outputs 4

---

Other Ways to Create an Array

If you are familiar with C#, you might have seen arrays created with the new keyword, and perhaps you have seen arrays with a specified size as well. In C#, there are different ways to create an array:

// Create an array of four elements, and add values later
string[] cars = new string[4];

// Create an array of four elements and add values right away 
string[] cars = new string[4] {"Volvo", "BMW", "Ford", "Mazda"};

// Create an array of four elements without specifying the size 
string[] cars = new string[] {"Volvo", "BMW", "Ford", "Mazda"};

// Create an array of four elements, omitting the new keyword, and without specifying the size
string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};

It is up to you which option you choose. In our tutorial, we will often use the last option, as it is faster and easier to read.

However, you should note that if you declare an array and initialize it later, you have to use the new keyword:

// Declare an array
string[] cars;

// Add values, using new
cars = new string[] {"Volvo", "BMW", "Ford"};

// Add values without using new (this will cause an error)
cars = {"Volvo", "BMW", "Ford"};

---

C# Exercises

Test Yourself With Exercises

Exercise:

Create an array of type string called cars.

  = {"Volvo", "BMW", "Ford", "Mazda"};

Submit Answer »

---

C# Loop Through Arrays

---

Loop Through an Array

You can loop through the array elements with the for loop, and use the Length property to specify how many times the loop should run.

The following example outputs all elements in the cars array:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
for (int i = 0; i < cars.Length; i++) 
{
  Console.WriteLine(cars[i]);
}

---

The foreach Loop

There is also a foreach loop, which is used exclusively to loop through elements in an array:

Syntax

foreach (type variableName in arrayName) 
{
  // code block to be executed
}

The following example outputs all elements in the cars array, using a foreach loop:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
foreach (string i in cars) 
{
  Console.WriteLine(i);
}

The example above can be read like this: for each string element (called i - as in index) in cars, print out the value of i.

If you compare the for loop and foreach loop, you will see that the foreach method is easier to write, it does not require a counter (using the Length property), and it is more readable.

---

C# Sort Arrays

---

Sort an Array

There are many array methods available, for example Sort(), which sorts an array alphabetically or in an ascending order:

Example

// Sort a string
string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Array.Sort(cars);
foreach (string i in cars)
{
  Console.WriteLine(i);
}

// Sort an int
int[] myNumbers = {5, 1, 8, 9};
Array.Sort(myNumbers);
foreach (int i in myNumbers)
{
  Console.WriteLine(i);
}

---

System.Linq Namespace

Other useful array methods, such as Min, Max, and Sum, can be found in the System.Linq namespace:

Example

using System;
using System.Linq;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int[] myNumbers = {5, 1, 8, 9};
      Console.WriteLine(myNumbers.Max());  // returns the largest value
      Console.WriteLine(myNumbers.Min());  // returns the smallest value
      Console.WriteLine(myNumbers.Sum());  // returns the sum of elements
    }
  }
}

You will learn more about other namespaces in a later chapter.

---

C# Multidimensional Arrays

---

Multidimensional Arrays

In the previous chapter, you learned about , which is also known as single dimension arrays. These are great, and something you will use a lot while programming in C#. However, if you want to store data as a tabular form, like a table with rows and columns, you need to get familiar with multidimensional arrays.

A multidimensional array is basically an array of arrays.

Arrays can have any number of dimensions. The most common are two-dimensional arrays (2D).

---

Two-Dimensional Arrays

To create a 2D array, add each array within its own set of curly braces, and insert a comma (,) inside the square brackets:

Example

int[,] numbers = { {1, 4, 2}, {3, 6, 8} };

Good to know: The single comma [,] specifies that the array is two-dimensional. A three-dimensional array would have two commas: int[,,].

numbers is now an array with two arrays as its elements. The first array element contains three elements: 1, 4 and 2, while the second array element contains 3, 6 and 8. To visualize it, think of the array as a table with rows and columns:

---

Access Elements of a 2D Array

To access an element of a two-dimensional array, you must specify two indexes: one for the array, and one for the element inside that array. Or better yet, with the table visualization in mind; one for the row and one for the column (see example below).

This statement accesses the value of the element in the first row (0) and third column (2) of the numbers array:

Example

int[,] numbers = { {1, 4, 2}, {3, 6, 8} };
Console.WriteLine(numbers[0, 2]);  // Outputs 2

Remember that: Array indexes start with 0: [0] is the first element. [1] is the second element, etc.

---

Change Elements of a 2D Array

You can also change the value of an element.

The following example will change the value of the element in the first row (0) and first column (0):

Example

int[,] numbers = { {1, 4, 2}, {3, 6, 8} };
numbers[0, 0] = 5;  // Change value to 5
Console.WriteLine(numbers[0, 0]); // Outputs 5 instead of 1

---

Loop Through a 2D Array

You can easily loop through the elements of a two-dimensional array with a foreach loop:

Example

int[,] numbers = { {1, 4, 2}, {3, 6, 8} };

foreach (int i in numbers)
{
  Console.WriteLine(i);
} 

You can also use a . For multidimensional arrays, you need one loop for each of the array's dimensions.

Also note that we have to use GetLength() instead of Length to specify how many times the loop should run:

Example

int[,] numbers = { {1, 4, 2}, {3, 6, 8} };

for (int i = 0; i < numbers.GetLength(0); i++) 
{ 
  for (int j = 0; j < numbers.GetLength(1); j++) 
  { 
    Console.WriteLine(numbers[i, j]); 
  } 
}  

---

C# Methods

---

A method is a block of code which only runs when it is called.

You can pass data, known as parameters, into a method.

Methods are used to perform certain actions, and they are also known as functions.

Why use methods? To reuse code: define the code once, and use it many times.

---

Create a Method

A method is defined with the name of the method, followed by parentheses (). C# provides some pre-defined methods, which you already are familiar with, such as Main(), but you can also create your own methods to perform certain actions:

Example

Create a method inside the Program class:

class Program
{
  static void MyMethod() 
  {
    // code to be executed
  }
}

Example Explained

• MyMethod() is the name of the method
• static means that the method belongs to the Program class and not an object of the Program class. You will learn more about objects and how to access methods through objects later in this tutorial.
• void means that this method does not have a return value. You will learn more about return values later in this chapter

Note: In C#, it is good practice to start with an uppercase letter when naming methods, as it makes the code easier to read.

---

Call a Method

To call (execute) a method, write the method's name followed by two parentheses () and a semicolon;

In the following example, MyMethod() is used to print a text (the action), when it is called:

Example

Inside Main(), call the myMethod() method:

static void MyMethod() 
{
  Console.WriteLine("I just got executed!");
}

static void Main(string[] args)
{
  MyMethod();
}

// Outputs "I just got executed!"

A method can be called multiple times:

Example

static void MyMethod() 
{
  Console.WriteLine("I just got executed!");
}

static void Main(string[] args)
{
  MyMethod();
  MyMethod();
  MyMethod();
}

// I just got executed!
// I just got executed!
// I just got executed!

---

C# Method Parameters

---

Parameters and Arguments

Information can be passed to methods as parameter. Parameters act as variables inside the method.

They are specified after the method name, inside the parentheses. You can add as many parameters as you want, just separate them with a comma.

The following example has a method that takes a string called fname as parameter. When the method is called, we pass along a first name, which is used inside the method to print the full name:

Example

static void MyMethod(string fname) 
{
  Console.WriteLine(fname + " Refsnes");
}

static void Main(string[] args)
{
  MyMethod("Liam");
  MyMethod("Jenny");
  MyMethod("Anja");
}

// Liam Refsnes
// Jenny Refsnes
// Anja Refsnes

When a parameter is passed to the method, it is called an argument. So, from the example above: fname is a parameter, while Liam, Jenny and Anja are arguments.

---

Multiple Parameters

You can have as many parameters as you like, just separate them with commas:

Example

static void MyMethod(string fname, int age) 
{
  Console.WriteLine(fname + " is " + age);
}

static void Main(string[] args)
{
  MyMethod("Liam", 5);
  MyMethod("Jenny", 8);
  MyMethod("Anja", 31);
}

// Liam is 5
// Jenny is 8
// Anja is 31

Note that when you are working with multiple parameters, the method call must have the same number of arguments as there are parameters, and the arguments must be passed in the same order.

---

C# Method Parameters

---

Parameters and Arguments

Information can be passed to methods as parameter. Parameters act as variables inside the method.

They are specified after the method name, inside the parentheses. You can add as many parameters as you want, just separate them with a comma.

The following example has a method that takes a string called fname as parameter. When the method is called, we pass along a first name, which is used inside the method to print the full name:

Example

static void MyMethod(string fname) 
{
  Console.WriteLine(fname + " Refsnes");
}

static void Main(string[] args)
{
  MyMethod("Liam");
  MyMethod("Jenny");
  MyMethod("Anja");
}

// Liam Refsnes
// Jenny Refsnes
// Anja Refsnes

When a parameter is passed to the method, it is called an argument. So, from the example above: fname is a parameter, while Liam, Jenny and Anja are arguments.

---

Multiple Parameters

You can have as many parameters as you like, just separate them with commas:

Example

static void MyMethod(string fname, int age) 
{
  Console.WriteLine(fname + " is " + age);
}

static void Main(string[] args)
{
  MyMethod("Liam", 5);
  MyMethod("Jenny", 8);
  MyMethod("Anja", 31);
}

// Liam is 5
// Jenny is 8
// Anja is 31

Note that when you are working with multiple parameters, the method call must have the same number of arguments as there are parameters, and the arguments must be passed in the same order.

---

C# Default Parameter Value

---

Default Parameter Value

You can also use a default parameter value, by using the equals sign (=).

If we call the method without an argument, it uses the default value ("Norway"):

Example

static void MyMethod(string country = "Norway") 
{
  Console.WriteLine(country);
}

static void Main(string[] args)
{
  MyMethod("Sweden");
  MyMethod("India");
  MyMethod();
  MyMethod("USA");
}

// Sweden
// India
// Norway
// USA

A parameter with a default value, is often known as an "optional parameter". From the example above, country is an optional parameter and "Norway" is the default value.

---

C# Return Values

---

Return Values

In the , we used the void keyword in all examples, which indicates that the method should not return a value.

If you want the method to return a value, you can use a primitive data type (such as int or double) instead of void, and use the return keyword inside the method:

Example

static int MyMethod(int x) 
{
  return 5 + x;
}

static void Main(string[] args)
{
  Console.WriteLine(MyMethod(3));
}

// Outputs 8 (5 + 3)

This example returns the sum of a method's two parameters:

Example

static int MyMethod(int x, int y) 
{
  return x + y;
}

static void Main(string[] args)
{
  Console.WriteLine(MyMethod(5, 3));
}

// Outputs 8 (5 + 3)

You can also store the result in a variable (recommended, as it is easier to read and maintain):

Example

static int MyMethod(int x, int y) 
{
  return x + y;
}

static void Main(string[] args)
{
  int z = MyMethod(5, 3);
  Console.WriteLine(z);
}

// Outputs 8 (5 + 3)

---

C# Named Arguments

---

Named Arguments

It is also possible to send arguments with the key: value syntax.

That way, the order of the arguments does not matter:

Example

static void MyMethod(string child1, string child2, string child3) 
{
  Console.WriteLine("The youngest child is: " + child3);
}

static void Main(string[] args)
{
  MyMethod(child3: "John", child1: "Liam", child2: "Liam");
}

// The youngest child is: John

---

C# Method Overloading

---

Method Overloading

With method overloading, multiple methods can have the same name with different parameters:

Example

int MyMethod(int x)
float MyMethod(float x)
double MyMethod(double x, double y)

Consider the following example, which have two methods that add numbers of different type:

Example

static int PlusMethodInt(int x, int y)
{
  return x + y;
}

static double PlusMethodDouble(double x, double y)
{
  return x + y;
}

static void Main(string[] args)
{
  int myNum1 = PlusMethodInt(8, 5);
  double myNum2 = PlusMethodDouble(4.3, 6.26);
  Console.WriteLine("Int: " + myNum1);
  Console.WriteLine("Double: " + myNum2);
}

Instead of defining two methods that should do the same thing, it is better to overload one.

In the example below, we overload the PlusMethod method to work for both int and double:

Example

static int PlusMethod(int x, int y)
{
  return x + y;
}

static double PlusMethod(double x, double y)
{
  return x + y;
}

static void Main(string[] args)
{
  int myNum1 = PlusMethod(8, 5);
  double myNum2 = PlusMethod(4.3, 6.26);
  Console.WriteLine("Int: " + myNum1);
  Console.WriteLine("Double: " + myNum2);
}

Note: Multiple methods can have the same name as long as the number and/or type of parameters are different.

---

C# OOP

---

C# - What is OOP?

OOP stands for Object-Oriented Programming.

Procedural programming is about writing procedures or methods that perform operations on the data, while object-oriented programming is about creating objects that contain both data and methods.

Object-oriented programming has several advantages over procedural programming:

• OOP is faster and easier to execute
• OOP provides a clear structure for the programs
• OOP helps to keep the C# code DRY "Don't Repeat Yourself", and makes the code easier to maintain, modify and debug
• OOP makes it possible to create full reusable applications with less code and shorter development time

Tip: The "Don't Repeat Yourself" (DRY) principle is about reducing the repetition of code. You should extract out the codes that are common for the application, and place them at a single place and reuse them instead of repeating it.

---

C# - What are Classes and Objects?

Classes and objects are the two main aspects of object-oriented programming.

Look at the following illustration to see the difference between class and objects:

class

Fruit

objects

Apple

Banana

Mango

Another example:

class

Car

objects

Volvo

Audi

Toyota

So, a class is a template for objects, and an object is an instance of a class.

When the individual objects are created, they inherit all the variables and methods from the class.

You will learn much more about in the next chapter.

---

C# Classes and Objects

---

Classes and Objects

You learned from the previous chapter that C# is an object-oriented programming language.

Everything in C# is associated with classes and objects, along with its attributes and methods. For example: in real life, a car is an object. The car has attributes, such as weight and color, and methods, such as drive and brake.

A Class is like an object constructor, or a "blueprint" for creating objects.

---

Create a Class

To create a class, use the class keyword:

Create a class named "Car" with a variable color:

class Car 
{
  string color = "red";
}

When a variable is declared directly in a class, it is often referred to as a field (or attribute).

It is not required, but it is a good practice to start with an uppercase first letter when naming classes. Also, it is common that the name of the C# file and the class matches, as it makes our code organized. However it is not required (like in Java).

---

---

Create an Object

An object is created from a class. We have already created the class named Car, so now we can use this to create objects.

To create an object of Car, specify the class name, followed by the object name, and use the keyword new:

Example

Create an object called "myObj" and use it to print the value of color:

class Car 
{
  string color = "red";

  static void Main(string[] args)
  {
    Car myObj = new Car();
    Console.WriteLine(myObj.color);
  }
}

Note that we use the dot syntax (.) to access variables/fields inside a class (myObj.color). You will learn more about fields in the next chapter.

---

C# Classes and Objects

---

Classes and Objects

You learned from the previous chapter that C# is an object-oriented programming language.

Everything in C# is associated with classes and objects, along with its attributes and methods. For example: in real life, a car is an object. The car has attributes, such as weight and color, and methods, such as drive and brake.

A Class is like an object constructor, or a "blueprint" for creating objects.

---

Create a Class

To create a class, use the class keyword:

Create a class named "Car" with a variable color:

class Car 
{
  string color = "red";
}

When a variable is declared directly in a class, it is often referred to as a field (or attribute).

It is not required, but it is a good practice to start with an uppercase first letter when naming classes. Also, it is common that the name of the C# file and the class matches, as it makes our code organized. However it is not required (like in Java).

---

---

Create an Object

An object is created from a class. We have already created the class named Car, so now we can use this to create objects.

To create an object of Car, specify the class name, followed by the object name, and use the keyword new:

Example

Create an object called "myObj" and use it to print the value of color:

class Car 
{
  string color = "red";

  static void Main(string[] args)
  {
    Car myObj = new Car();
    Console.WriteLine(myObj.color);
  }
}

Note that we use the dot syntax (.) to access variables/fields inside a class (myObj.color). You will learn more about fields in the next chapter.

---

C# Multiple Classes and Objects

---

Multiple Objects

You can create multiple objects of one class:

Example

Create two objects of Car:

class Car
{
  string color = "red";
  static void Main(string[] args)
  {
    Car myObj1 = new Car();
    Car myObj2 = new Car();
    Console.WriteLine(myObj1.color);
    Console.WriteLine(myObj2.color);
  }
}

---

Using Multiple Classes

You can also create an object of a class and access it in another class. This is often used for better organization of classes (one class has all the fields and methods, while the other class holds the Main() method (code to be executed)).

• prog2.cs
• prog.cs

prog2.cs

class Car 
{
  public string color = "red";
}

prog.cs

class Program
{
  static void Main(string[] args)
  {
    Car myObj = new Car();
    Console.WriteLine(myObj.color);
  }
}

Did you notice the public keyword? It is called an access modifier, which specifies that the color variable/field of Car is accessible for other classes as well, such as Program.

You will learn much more about access modifiers and classes/objects in the next chapters.

---

C# Class Members

---

Class Members

Fields and methods inside classes are often referred to as "Class Members":

Example

Create a Car class with three class members: two fields and one method.

// The class
class MyClass
{
  // Class members
  string color = "red";        // field
  int maxSpeed = 200;          // field
  public void fullThrottle()   // method
  {
    Console.WriteLine("The car is going as fast as it can!");
  }
}

---

Fields

In the previous chapter, you learned that variables inside a class are called fields, and that you can access them by creating an object of the class, and by using the dot syntax (.).

The following example will create an object of the Car class, with the name myObj. Then we print the value of the fields color and maxSpeed:

Example

class Car 
{
  string color = "red";
  int maxSpeed = 200;

  static void Main(string[] args)
  {
    Car myObj = new Car();
    Console.WriteLine(myObj.color);
    Console.WriteLine(myObj.maxSpeed);
  }
}

You can also leave the fields blank, and modify them when creating the object:

Example

class Car 
{
  string color;
  int maxSpeed;

  static void Main(string[] args)
  {
    Car myObj = new Car();
    myObj.color = "red";
    myObj.maxSpeed = 200;
    Console.WriteLine(myObj.color);
    Console.WriteLine(myObj.maxSpeed);
  }
}

This is especially useful when creating multiple objects of one class:

Example

class Car 
{
  string model;
  string color;
  int year;

  static void Main(string[] args)
  {
    Car Ford = new Car();
    Ford.model = "Mustang";
    Ford.color = "red";
    Ford.year = 1969;

    Car Opel = new Car();
    Opel.model = "Astra";
    Opel.color = "white";
    Opel.year = 2005;

    Console.WriteLine(Ford.model);
    Console.WriteLine(Opel.model);
  }
}

---

---

Object Methods

You learned from the chapter that methods are used to perform certain actions.

Methods normally belong to a class, and they define how an object of a class behaves.

Just like with fields, you can access methods with the dot syntax. However, note that the method must be public. And remember that we use the name of the method followed by two parentheses () and a semicolon ; to call (execute) the method:

Example

class Car 
{
  string color;                 // field
  int maxSpeed;                 // field
  public void fullThrottle()    // method
  {
    Console.WriteLine("The car is going as fast as it can!"); 
  }

  static void Main(string[] args)
  {
    Car myObj = new Car();
    myObj.fullThrottle();  // Call the method
  }
}

Why did we declare the method as public, and not static, like in the examples from the ?

The reason is simple: a static method can be accessed without creating an object of the class, while public methods can only be accessed by objects.

---

Use Multiple Classes

Remember from the last chapter, that we can use multiple classes for better organization (one for fields and methods, and another one for execution). This is recommended:

prog2.cs

class Car 
{
  public string model;
  public string color;
  public int year;
  public void fullThrottle()
  {
    Console.WriteLine("The car is going as fast as it can!"); 
  }
}

prog.cs

class Program
{
  static void Main(string[] args)
  {
    Car Ford = new Car();
    Ford.model = "Mustang";
    Ford.color = "red";
    Ford.year = 1969;

    Car Opel = new Car();
    Opel.model = "Astra";
    Opel.color = "white";
    Opel.year = 2005;

    Console.WriteLine(Ford.model);
    Console.WriteLine(Opel.model);
  }
}

The public keyword is called an access modifier, which specifies that the fields of Car are accessible for other classes as well, such as Program.

You will learn more about in a later chapter.

Tip: As you continue to read, you will also learn more about other class members, such as and .

---

C# Constructors

---

Constructors

A constructor is a special method that is used to initialize objects. The advantage of a constructor, is that it is called when an object of a class is created. It can be used to set initial values for fields:

Example

Create a constructor:

// Create a Car class
class Car
{
  public string model;  // Create a field

  // Create a class constructor for the Car class
  public Car()
  {
    model = "Mustang"; // Set the initial value for model
  }

  static void Main(string[] args)
  {
    Car Ford = new Car();  // Create an object of the Car Class (this will call the constructor)
    Console.WriteLine(Ford.model);  // Print the value of model
  }
}

// Outputs "Mustang"

Note that the constructor name must match the class name, and it cannot have a return type (like void or int).

Also note that the constructor is called when the object is created.

All classes have constructors by default: if you do not create a class constructor yourself, C# creates one for you. However, then you are not able to set initial values for fields.

Constructors save time! Take a look at the last example on this page to really understand why.

---

---

Constructor Parameters

Constructors can also take parameters, which is used to initialize fields.

The following example adds a string modelName parameter to the constructor. Inside the constructor we set model to modelName (model=modelName). When we call the constructor, we pass a parameter to the constructor ("Mustang"), which will set the value of model to "Mustang":

Example

class Car
{
  public string model;

  // Create a class constructor with a parameter
  public Car(string modelName)
  {
    model = modelName;
  }

  static void Main(string[] args)
  {
    Car Ford = new Car("Mustang");
    Console.WriteLine(Ford.model);
  }
}

// Outputs "Mustang"

You can have as many parameters as you want:

Example

class Car
{
  public string model;
  public string color;
  public int year;

  // Create a class constructor with multiple parameters
  public Car(string modelName, string modelColor, int modelYear)
  {
    model = modelName;
    color = modelColor;
    year = modelYear;
  }

  static void Main(string[] args)
  {
    Car Ford = new Car("Mustang", "Red", 1969);
    Console.WriteLine(Ford.color + " " + Ford.year + " " + Ford.model);
  }
}


// Outputs Red 1969 Mustang

Tip: Just like other methods, constructors can be overloaded by using different numbers of parameters.

---

Constructors Save Time

When you consider the example from the previous chapter, you will notice that constructors are very useful, as they help reducing the amount of code:

Without constructor:

prog.cs

class Program
{
  static void Main(string[] args)
  {
    Car Ford = new Car();
    Ford.model = "Mustang";
    Ford.color = "red";
    Ford.year = 1969;

    Car Opel = new Car();
    Opel.model = "Astra";
    Opel.color = "white";
    Opel.year = 2005;

    Console.WriteLine(Ford.model);
    Console.WriteLine(Opel.model);
  }
}

With constructor:

prog.cs

class Program
{
  static void Main(string[] args)
  {
    Car Ford = new Car("Mustang", "Red", 1969);
    Car Opel = new Car("Astra", "White", 2005);

    Console.WriteLine(Ford.model);
    Console.WriteLine(Opel.model);
  }
}

C# Access Modifiers

---

Access Modifiers

By now, you are quite familiar with the public keyword that appears in many of our examples:

public string color;

The public keyword is an access modifier, which is used to set the access level/visibility for classes, fields, methods and properties.

C# has the following access modifiers:

Modifier	Description
public	The code is accessible for all classes
private	The code is only accessible within the same class
protected	The code is accessible within the same class, or in a class that is inherited from that class. You will learn more about in a later chapter
internal	The code is only accessible within its own assembly, but not from another assembly. You will learn more about this in a later chapter

There's also two combinations: protected internal and private protected.

For now, lets focus on public and private modifiers.

---

Private Modifier

If you declare a field with a private access modifier, it can only be accessed within the same class:

Example

class Car
{
  private string model = "Mustang";

  static void Main(string[] args)
  {
    Car myObj = new Car();
    Console.WriteLine(myObj.model);
  }
}

The output will be:

Mustang

If you try to access it outside the class, an error will occur:

Example

class Car
{
  private string model = "Mustang";
}

class Program
{
  static void Main(string[] args)
  {
    Car myObj = new Car();
    Console.WriteLine(myObj.model);
  }
}

The output will be:

'Car.model' is inaccessible due to its protection level
The field 'Car.model' is assigned but its value is never used

---

---

Public Modifier

If you declare a field with a public access modifier, it is accessible for all classes:

Example

class Car
{
  public string model = "Mustang";
}

class Program
{
  static void Main(string[] args)
  {
    Car myObj = new Car();
    Console.WriteLine(myObj.model);
  }
}

The output will be:

Mustang

---

Why Access Modifiers?

To control the visibility of class members (the security level of each individual class and class member).

To achieve "Encapsulation" - which is the process of making sure that "sensitive" data is hidden from users. This is done by declaring fields as private. You will learn more about this in the next chapter.

Note: By default, all members of a class are private if you don't specify an access modifier:

Example

class Car
{
  string model;  // private
  string year;   // private
}

---

C# Properties (Get and Set)

---

Properties and Encapsulation

Before we start to explain properties, you should have a basic understanding of "Encapsulation".

The meaning of Encapsulation, is to make sure that "sensitive" data is hidden from users. To achieve this, you must:

• declare fields/variables as private
• provide public get and set methods, through properties, to access and update the value of a private field

---

Properties

You learned from the previous chapter that private variables can only be accessed within the same class (an outside class has no access to it). However, sometimes we need to access them - and it can be done with properties.

A property is like a combination of a variable and a method, and it has two methods: a get and a set method:

Example

class Person
{
  private string name; // field

  public string Name   // property
  {
    get { return name; }   // get method
    set { name = value; }  // set method
  }
}

Example explained

The Name property is associated with the name field. It is a good practice to use the same name for both the property and the private field, but with an uppercase first letter.

The get method returns the value of the variable name.

The set method assigns a value to the name variable. The value keyword represents the value we assign to the property.

If you don't fully understand it, take a look at the example below.

Now we can use the Name property to access and update the private field of the Person class:

Example

class Person
{
  private string name; // field
  public string Name   // property
  {
    get { return name; }
    set { name = value; }
  }
}

class Program
{
  static void Main(string[] args)
  {
    Person myObj = new Person();
    myObj.Name = "Liam";
    Console.WriteLine(myObj.Name);
  }
}

The output will be:

Liam

---

---

Automatic Properties (Short Hand)

C# also provides a way to use short-hand / automatic properties, where you do not have to define the field for the property, and you only have to write get; and set; inside the property.

The following example will produce the same result as the example above. The only difference is that there is less code:

Example

Using automatic properties:

class Person
{
  public string Name  // property
  { get; set; }
}

class Program
{
  static void Main(string[] args)
  {
    Person myObj = new Person();
    myObj.Name = "Liam";
    Console.WriteLine(myObj.Name);
  }
}

The output will be:

Liam

---

Why Encapsulation?

• Better control of class members (reduce the possibility of yourself (or others) to mess up the code)
• Fields can be made read-only (if you only use the get method), or write-only (if you only use the set method)
• Flexible: the programmer can change one part of the code without affecting other parts
• Increased security of data

---

C# Inheritance

---

Inheritance (Derived and Base Class)

In C#, it is possible to inherit fields and methods from one class to another. We group the "inheritance concept" into two categories:

• Derived Class (child) - the class that inherits from another class
• Base Class (parent) - the class being inherited from

To inherit from a class, use the : symbol.

In the example below, the Car class (child) inherits the fields and methods from the Vehicle class (parent):

Example

class Vehicle  // base class (parent) 
{
  public string brand = "Ford";  // Vehicle field
  public void honk()             // Vehicle method 
  {                    
    Console.WriteLine("Tuut, tuut!");
  }
}

class Car : Vehicle  // derived class (child)
{
  public string modelName = "Mustang";  // Car field
}

class Program
{
  static void Main(string[] args)
  {
    // Create a myCar object
    Car myCar = new Car();

    // Call the honk() method (From the Vehicle class) on the myCar object
    myCar.honk();

    // Display the value of the brand field (from the Vehicle class) and the value of the modelName from the Car class
    Console.WriteLine(myCar.brand + " " + myCar.modelName);
  }
}

Why And When To Use "Inheritance"?

- It is useful for code reusability: reuse fields and methods of an existing class when you create a new class.

Tip: Also take a look at the next chapter, , which uses inherited methods to perform different tasks.

---

The sealed Keyword

If you don't want other classes to inherit from a class, use the sealed keyword:

If you try to access a sealed class, C# will generate an error:

sealed class Vehicle 
{
  ...
}

class Car : Vehicle 
{
  ...
}

The error message will be something like this:

'Car': cannot derive from sealed type 'Vehicle'

---

C# Polymorphism

---

Polymorphism and Overriding Methods

Polymorphism means "many forms", and it occurs when we have many classes that are related to each other by inheritance.

Like we specified in the previous chapter; lets us inherit fields and methods from another class. Polymorphism uses those methods to perform different tasks. This allows us to perform a single action in different ways.

For example, think of a base class called Animal that has a method called animalSound(). Derived classes of Animals could be Pigs, Cats, Dogs, Birds - And they also have their own implementation of an animal sound (the pig oinks, and the cat meows, etc.):

Example

class Animal  // Base class (parent) 
{
  public void animalSound() 
  {
    Console.WriteLine("The animal makes a sound");
  }
}

class Pig : Animal  // Derived class (child) 
{
  public void animalSound() 
  {
    Console.WriteLine("The pig says: wee wee");
  }
}

class Dog : Animal  // Derived class (child) 
{
  public void animalSound() 
  {
    Console.WriteLine("The dog says: bow wow");
  }
}

Remember from the that we use the : symbol to inherit from a class.

Now we can create Pig and Dog objects and call the animalSound() method on both of them:

Example

class Animal  // Base class (parent) 
{
  public void animalSound() 
  {
    Console.WriteLine("The animal makes a sound");
  }
}

class Pig : Animal  // Derived class (child) 
{
  public void animalSound() 
  {
    Console.WriteLine("The pig says: wee wee");
  }
}

class Dog : Animal  // Derived class (child) 
{
  public void animalSound() 
  {
    Console.WriteLine("The dog says: bow wow");
  }
}

class Program 
{
  static void Main(string[] args) 
  {
    Animal myAnimal = new Animal();  // Create a Animal object
    Animal myPig = new Pig();  // Create a Pig object
    Animal myDog = new Dog();  // Create a Dog object

    myAnimal.animalSound();
    myPig.animalSound();
    myDog.animalSound();
  }
}

The output will be:

The animal makes a sound
The animal makes a sound
The animal makes a sound

Not The Output I Was Looking For

The output from the example above was probably not what you expected. That is because the base class method overrides the derived class method, when they share the same name.

However, C# provides an option to override the base class method, by adding the virtual keyword to the method inside the base class, and by using the override keyword for each derived class methods:

Example

class Animal  // Base class (parent) 
{
  public virtual void animalSound() 
  {
    Console.WriteLine("The animal makes a sound");
  }
}

class Pig : Animal  // Derived class (child) 
{
  public override void animalSound() 
  {
    Console.WriteLine("The pig says: wee wee");
  }
}

class Dog : Animal  // Derived class (child) 
{
  public override void animalSound() 
  {
    Console.WriteLine("The dog says: bow wow");
  }
}

class Program 
{
  static void Main(string[] args) 
  {
    Animal myAnimal = new Animal();  // Create a Animal object
    Animal myPig = new Pig();  // Create a Pig object
    Animal myDog = new Dog();  // Create a Dog object

    myAnimal.animalSound();
    myPig.animalSound();
    myDog.animalSound();
  }
}

The output will be:

The animal makes a sound
The pig says: wee wee
The dog says: bow wow

Why And When To Use "Inheritance" and "Polymorphism"?

- It is useful for code reusability: reuse fields and methods of an existing class when you create a new class.

C# Abstraction

---

Abstract Classes and Methods

Data abstraction is the process of hiding certain details and showing only essential information to the user.
Abstraction can be achieved with either abstract classes or (which you will learn more about in the next chapter).

The abstract keyword is used for classes and methods:

• Abstract class: is a restricted class that cannot be used to create objects (to access it, it must be inherited from another class).


• Abstract method: can only be used in an abstract class, and it does not have a body. The body is provided by the derived class (inherited from).

An abstract class can have both abstract and regular methods:

abstract class Animal 
{
  public abstract void animalSound();
  public void sleep() 
  {
    Console.WriteLine("Zzz");
  }
}

From the example above, it is not possible to create an object of the Animal class:

Animal myObj = new Animal(); // Will generate an error (Cannot create an instance of the abstract class or interface 'Animal')

To access the abstract class, it must be inherited from another class. Let's convert the Animal class we used in the chapter to an abstract class.

Remember from the that we use the : symbol to inherit from a class, and that we use the override keyword to override the base class method.

Example

// Abstract class
abstract class Animal
{
  // Abstract method (does not have a body)
  public abstract void animalSound();
  // Regular method
  public void sleep()
  {
    Console.WriteLine("Zzz");
  }
}

// Derived class (inherit from Animal)
class Pig : Animal
{
  public override void animalSound()
  {
    // The body of animalSound() is provided here
    Console.WriteLine("The pig says: wee wee");
  }
}

class Program
{
  static void Main(string[] args)
  {
    Pig myPig = new Pig(); // Create a Pig object
    myPig.animalSound();  // Call the abstract method
    myPig.sleep();  // Call the regular method
  }
}

Why And When To Use Abstract Classes and Methods?

To achieve security - hide certain details and only show the important details of an object.

Note: Abstraction can also be achieved with , which you will learn more about in the next chapter.

C# Interface

---

Interfaces

Another way to achieve in C#, is with interfaces.

An interface is a completely "abstract class", which can only contain abstract methods and properties (with empty bodies):

Example

// interface
interface Animal 
{
  void animalSound(); // interface method (does not have a body)
  void run(); // interface method (does not have a body)
}

It is considered good practice to start with the letter "I" at the beginning of an interface, as it makes it easier for yourself and others to remember that it is an interface and not a class.

By default, members of an interface are abstract and public.

Note: Interfaces can contain properties and methods, but not fields.

To access the interface methods, the interface must be "implemented" (kinda like inherited) by another class. To implement an interface, use the : symbol (just like with inheritance). The body of the interface method is provided by the "implement" class. Note that you do not have to use the override keyword when implementing an interface:

Example

// Interface
interface IAnimal 
{
  void animalSound(); // interface method (does not have a body)
}

// Pig "implements" the IAnimal interface
class Pig : IAnimal 
{
  public void animalSound() 
  {
    // The body of animalSound() is provided here
    Console.WriteLine("The pig says: wee wee");
  }
}

class Program 
{
  static void Main(string[] args) 
  {
    Pig myPig = new Pig();  // Create a Pig object
    myPig.animalSound();
  }
}

Notes on Interfaces:

• Like abstract classes, interfaces cannot be used to create objects (in the example above, it is not possible to create an "IAnimal" object in the Program class)
• Interface methods do not have a body - the body is provided by the "implement" class
• On implementation of an interface, you must override all of its methods
• Interfaces can contain properties and methods, but not fields/variables
• Interface members are by default abstract and public
• An interface cannot contain a constructor (as it cannot be used to create objects)

Why And When To Use Interfaces?

1) To achieve security - hide certain details and only show the important details of an object (interface).

2) C# does not support "multiple inheritance" (a class can only inherit from one base class). However, it can be achieved with interfaces, because the class can implement multiple interfaces. Note: To implement multiple interfaces, separate them with a comma (see example below).

---

C# Interface

---

Interfaces

Another way to achieve in C#, is with interfaces.

An interface is a completely "abstract class", which can only contain abstract methods and properties (with empty bodies):

Example

// interface
interface Animal 
{
  void animalSound(); // interface method (does not have a body)
  void run(); // interface method (does not have a body)
}

It is considered good practice to start with the letter "I" at the beginning of an interface, as it makes it easier for yourself and others to remember that it is an interface and not a class.

By default, members of an interface are abstract and public.

Note: Interfaces can contain properties and methods, but not fields.

To access the interface methods, the interface must be "implemented" (kinda like inherited) by another class. To implement an interface, use the : symbol (just like with inheritance). The body of the interface method is provided by the "implement" class. Note that you do not have to use the override keyword when implementing an interface:

Example

// Interface
interface IAnimal 
{
  void animalSound(); // interface method (does not have a body)
}

// Pig "implements" the IAnimal interface
class Pig : IAnimal 
{
  public void animalSound() 
  {
    // The body of animalSound() is provided here
    Console.WriteLine("The pig says: wee wee");
  }
}

class Program 
{
  static void Main(string[] args) 
  {
    Pig myPig = new Pig();  // Create a Pig object
    myPig.animalSound();
  }
}

Notes on Interfaces:

• Like abstract classes, interfaces cannot be used to create objects (in the example above, it is not possible to create an "IAnimal" object in the Program class)
• Interface methods do not have a body - the body is provided by the "implement" class
• On implementation of an interface, you must override all of its methods
• Interfaces can contain properties and methods, but not fields/variables
• Interface members are by default abstract and public
• An interface cannot contain a constructor (as it cannot be used to create objects)

Why And When To Use Interfaces?

1) To achieve security - hide certain details and only show the important details of an object (interface).

2) C# does not support "multiple inheritance" (a class can only inherit from one base class). However, it can be achieved with interfaces, because the class can implement multiple interfaces. Note: To implement multiple interfaces, separate them with a comma (see example below).

---

C# Multiple Interfaces

---

Multiple Interfaces

To implement multiple interfaces, separate them with a comma:

Example

interface IFirstInterface 
{
  void myMethod(); // interface method
}

interface ISecondInterface 
{
  void myOtherMethod(); // interface method
}

// Implement multiple interfaces
class DemoClass : IFirstInterface, ISecondInterface 
{
  public void myMethod() 
  {
    Console.WriteLine("Some text..");
  }
  public void myOtherMethod() 
  {
    Console.WriteLine("Some other text...");
  }
}

class Program 
{
  static void Main(string[] args)
  {
    DemoClass myObj = new DemoClass();
    myObj.myMethod();
    myObj.myOtherMethod();
  }
}

C# Enum

---

C# Enums

An enum is a special "class" that represents a group of constants (unchangeable/read-only variables).

To create an enum, use the enum keyword (instead of class or interface), and separate the enum items with a comma:

Example

enum Level 
{
  Low,
  Medium,
  High
}

You can access enum items with the dot syntax:

Level myVar = Level.Medium;
Console.WriteLine(myVar);

Enum is short for "enumerations", which means "specifically listed".

---

Enum inside a Class

You can also have an enum inside a class:

Example

class Program
{
  enum Level
  {
    Low,
    Medium,
    High
  }
  static void Main(string[] args)
  {
    Level myVar = Level.Medium;
    Console.WriteLine(myVar);
  }
}

The output will be:

Medium

---

---

Enum Values

By default, the first item of an enum has the value 0. The second has the value 1, and so on.

To get the integer value from an item, you must the item to an int:

Example

enum Months
{
  January,    // 0
  February,   // 1
  March,      // 2
  April,      // 3
  May,        // 4
  June,       // 5
  July        // 6
}

static void Main(string[] args)
{
  int myNum = (int) Months.April;
  Console.WriteLine(myNum);
}

The output will be:

3

You can also assign your own enum values, and the next items will update their numbers accordingly:

Example

enum Months
{
  January,    // 0
  February,   // 1
  March=6,    // 6
  April,      // 7
  May,        // 8
  June,       // 9
  July        // 10
}

static void Main(string[] args)
{
  int myNum = (int) Months.April;
  Console.WriteLine(myNum);
}

The output will be:

7

---

Enum in a Switch Statement

Enums are often used in switch statements to check for corresponding values:

Example

enum Level 
{
  Low,
  Medium,
  High
}

static void Main(string[] args) 
{
  Level myVar = Level.Medium;
  switch(myVar) 
  {
    case Level.Low:
      Console.WriteLine("Low level");
      break;
    case Level.Medium:
       Console.WriteLine("Medium level");
      break;
    case Level.High:
      Console.WriteLine("High level");
      break;
  }
}

The output will be:

Medium level

Why And When To Use Enums?

Use enums when you have values that you know aren't going to change, like month days, days, colors, deck of cards, etc.

C# Files

---

Working With Files

The File class from the System.IO namespace, allows us to work with files:

Example

using System.IO;  // include the System.IO namespace

File.SomeFileMethod();  // use the file class with methods

The File class has many useful methods for creating and getting information about files. For example:

Method	Description
AppendText()	Appends text at the end of an existing file
Copy()	Copies a file
Create()	Creates or overwrites a file
Delete()	Deletes a file
Exists()	Tests whether the file exists
ReadAllText()	Reads the contents of a file
Replace()	Replaces the contents of a file with the contents of another file
WriteAllText()	Creates a new file and writes the contents to it. If the file already exists, it will be overwritten.

For a full list of File methods, go to .

---

Write To a File and Read It

In the following example, we use the WriteAllText() method to create a file named "filename.txt" and write some content to it. Then we use the ReadAllText() method to read the contents of the file:

Example

using System.IO;  // include the System.IO namespace

string writeText = "Hello World!";  // Create a text string
File.WriteAllText("filename.txt", writeText);  // Create a file and write the content of writeText to it

string readText = File.ReadAllText("filename.txt");  // Read the contents of the file
Console.WriteLine(readText);  // Output the content

The output will be:

Hello World!

---

C# Exceptions - Try..Catch

---

C# Exceptions

When executing C# code, different errors can occur: coding errors made by the programmer, errors due to wrong input, or other unforeseeable things.

When an error occurs, C# will normally stop and generate an error message. The technical term for this is: C# will throw an exception (throw an error).

---

C# try and catch

The try statement allows you to define a block of code to be tested for errors while it is being executed.

The catch statement allows you to define a block of code to be executed, if an error occurs in the try block.

The try and catch keywords come in pairs:

Syntax

try 
{
  //  Block of code to try
}
catch (Exception e)
{
  //  Block of code to handle errors
}

Consider the following example, where we create an array of three integers:

This will generate an error, because myNumbers[10] does not exist.

int[] myNumbers = {1, 2, 3};
Console.WriteLine(myNumbers[10]); // error!

The error message will be something like this:

System.IndexOutOfRangeException: 'Index was outside the bounds of the array.'

If an error occurs, we can use try...catch to catch the error and execute some code to handle it.

In the following example, we use the variable inside the catch block (e) together with the built-in Message property, which outputs a message that describes the exception:

Example

try
{
  int[] myNumbers = {1, 2, 3};
  Console.WriteLine(myNumbers[10]);
}
catch (Exception e)
{
  Console.WriteLine(e.Message);
}

The output will be:

Index was outside the bounds of the array.

You can also output your own error message:

Example

try
{
  int[] myNumbers = {1, 2, 3};
  Console.WriteLine(myNumbers[10]);
}
catch (Exception e)
{
  Console.WriteLine("Something went wrong.");
}

The output will be:

Something went wrong.

---

---

Finally

The finally statement lets you execute code, after try...catch, regardless of the result:

Example

try
{
  int[] myNumbers = {1, 2, 3};
  Console.WriteLine(myNumbers[10]);
}
catch (Exception e)
{
  Console.WriteLine("Something went wrong.");
}
finally
{
  Console.WriteLine("The 'try catch' is finished.");
}

The output will be:

Something went wrong.
The 'try catch' is finished.

---

The throw keyword

The throw statement allows you to create a custom error.

The throw statement is used together with an exception class. There are many exception classes available in C#: ArithmeticException, FileNotFoundException, IndexOutOfRangeException, TimeOutException, etc:

Example

static void checkAge(int age)
{
  if (age < 18)
  {
    throw new ArithmeticException("Access denied - You must be at least 18 years old.");
  }
  else
  {
    Console.WriteLine("Access granted - You are old enough!");
  }
}

static void Main(string[] args)
{
  checkAge(15);
}

The error message displayed in the program will be:

System.ArithmeticException: 'Access denied - You must be at least 18 years old.'

If age was 20, you would not get an exception:

Example

checkAge(20);

The output will be:

Access granted - You are old enough!

---

C# How To Add Two Numbers

---

Add Two Numbers

Learn how to add two numbers in C#:

Example

int x = 5;
int y = 6;
int sum = x + y;
Console.WriteLine(sum); // Print the sum of x + y

---

C# Examples

---

C# Syntax

---

C# Comments

---

C# Variables

---

C# Data Types

---

C# Type Casting

---

C# User Input

---

C# Operators

---

C# Math

---

C# Strings

---

C# Booleans

---

---

C# If...Else (Conditions)

---

C# Switch

---

C# Loops

---

C# Arrays

---

C# Methods

---

C# Classes and Objects

---

C# Exceptions (Try...Catch)

---

C# Online Compiler

---

C# Compiler (Editor)

With our online C# compiler, you can edit C# code, and view the result in your browser.

Example

using System;

namespace HelloWorld
{
  class Program
  {
    static void Main(string[] args)
    {
      Console.WriteLine("Hello World!");    
    }
  }
}

Hello World!

Click on the "Try it Yourself" button to see how it works.

---

Publish Your Code

If you want to create your own C# applications, check out .

is a website-building tool that enables you to create and share your own website, as well as develop and host C# applications.

You can change the website's look and how it works by editing the code right in your web browser.

It's easy to use and doesn't require any setup.

The code editor is packed with features to help you achieve more:

• Templates: Start from scratch or use a template
• Cloud-based: no installations required. You only need your browser
• Terminal & Log: debug and troubleshoot your code easily
• File Navigator: switch between files inside the code editor
• And much more!

---

Learn Faster

Practice is key to mastering coding, and the best way to put your C# knowledge into practice is by getting practical with code.

Use to build, test and deploy code.

The code editor lets you write and practice different types of computer languages. It includes C#, but you can use it for other languages too:

If you don't know C#, we suggest that you read our from scratch.

---

Easy Package Management

Get an overview of your packages and easily add or delete frameworks and libraries. Then, with just one click, you can make changes to your packages without manual installation.

---

Build Powerful Websites

You can also use the code editor in to build frontend or full-stack websites from scratch.

Or you can use the 60+ templates available and save time:

Create your Spaces account today and explore them all!

---

Share Your Website With The World

Host and publish your websites in no time with .

W3Schools subdomain and SSL certificate are included for free with . An SSL certificate makes your website safe and secure. It also helps people trust your website and makes it easier to find it online.

Want a custom domain for your website?

You can buy a domain or transfer an existing one and connect it to your space.

---

How Does It Work?

Get started in a few clicks with .

---

C# Exercises

---

You can test your C# skills with W3Schools' Exercises.

---

Exercises

We have gathered a variety of C# exercises (with answers) for each C# Chapter.

Try to solve an exercise by editing some code, or show the answer to see what you've done wrong.

Count Your Score

You will get 1 point for each correct answer. Your score and total score will always be displayed.

Start C# Exercises

Good luck!

If you don't know C#, we suggest that you read our from scratch.

---

Kickstart your career

Get certified by completing the course

C# Quiz

---

You can test your C# skills with W3Schools' Quiz.

---

The Test

The test contains 25 questions and there is no time limit.

The test is not official, it's just a nice way to see how much you know, or don't know, about C#.

Count Your Score

You will get 1 point for each correct answer. At the end of the Quiz, your total score will be displayed. Maximum score is 25 points.

Start the Quiz

Good luck!

If you don't know C#, we suggest that you read our from scratch.

---

Kickstart your career

Get certified by completing the course

C# Certification

---

W3Schools offers an Online Certification Program. The perfect solution for busy professionals who need to balance work, family, and career building. More than 50 000 certificates already issued!

W3Schools offers an Online Certification Program.

The perfect solution for busy professionals who need to balance work, family, and career building.

More than 50 000 certificates already issued!

Document your skills
Improve your career

Study at your own pace
Save time and money

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Trusted by top companies

---

Who Should Consider Getting Certified?

Any student or professional within the digital industry.

Certifications are valuable assets to gain trust and demonstrate knowledge to your clients, current or future employers on a ever increasing competitive market.

---

W3Schools is Trusted by Top Companies

W3Schools has over two decades of experience with teaching coding online.

Our certificates are recognized and valued by companies looking to employ skilled developers.

---

Save Time and Money

Show the world your coding skills by getting a certification.

The prices is a small fraction compared to the price of traditional education.

Document and validate your competence by getting certified!

Exam overview

Fee: 45 USD

Number of questions: 50

Requirement to pass: 75% correct answers

Time limit: 50 minutes

Number of attempts to pass: Two

Exam deadline: None

Certification Expiration: None

Format: Online, multiple choice

---

Advance Faster in Your Career

Getting a certificate proves your commitment to upgrading your skills.

The certificate can be added as credentials to your CV, Resume, LinkedIn profile, and so on.

It gives you the credibility needed for more responsibilities, larger projects, and a higher salary.

Knowledge is power, especially in the current job market.

Documentation of your skills enables you to advance your career or helps you to start a new one.

---

How Does It Work?

• Study for free at W3Schools.com
• Study at your own speed
• Test your skills with W3Schools online quizzes
• Apply for your certificate by paying an exam fee
• Take your exam online, at any time, and from any location

---

Get Your Certificate and Share It With The World

Example certificate:

Each certificate gets a unique link that can be shared with others.

Validate your certification with the link or QR code.

Check how it looks like in this .

Share your certificate on LinkedIn in the Certifications section in just one click!

---

Document Your Skills

Getting a certificate proves your commitment to upgrade your skills, gives you the credibility needed for more responsibilities, larger projects, and a higher salary.

---

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We are working with schools, companies and organizations from all over the world.

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