VB.NET Functions

In VB.NET, the function is a separate group of codes that are used to perform a specific task when the defined function is called in a program. After the execution of a function, control transfer to the main() method for further execution. It returns a value. In VB.NET, we can create more than one function in a program to perform various functionalities. The function is also useful to code reusability by reducing the duplicity of the code. For example, if we need to use the same functionality at multiple places in a program, we can simply create a function and call it whenever required.

Defining a Function

The syntax to define a function is:

[Access_specifier ] Function Function_Name [ (ParameterList) ] As Return_Type
[ Block of Statement ]
Return return_val
End Function

Where,

Access_Specifier: It defines the access level of the function such as public, private, or friend, Protected function to access the method.
Function_Name: The function_name indicate the name of the function that should be unique.
ParameterList: It defines the list of the parameters to send or retrieve data from a method.
Return_Type: It defines the data type of the variable that returns by the function.

The following are the various ways to define the function in a VB.NET.

Public Function add() As Integer
' Statement to be executed
End Function

Private Function GetData( ByVal username As String) As String
' Statement to be executed
End Function

Public Function GetData( ByVal username As String, ByVal userId As Integer) As String
' Statement to be executed
End Function

Example: Write a program to find the sum and subtraction of two numbers using the function.

Find_Sum.vb

Imports System
Module Find_Sum
    ' Create the SumOfTwo() Function and pass the parameters.
    Function SumOfTwo(ByVal n1 As Integer, ByVal n2 As Integer) As Integer
        ' Define the local variable.
        Dim sum As Integer = 0
        sum = n1 + n2
        Return sum
    End Function
    Function SubtractionOfTwo(ByVal n1 As Integer, ByVal n2 As Integer) As Integer
        ' Define the local variable.
        Dim subtract As Integer
        subtract = n1 - n2
        Return subtract
    End Function
    Sub Main()
        ' Define the local variable a and b.
        Dim a As Integer = 50
        Dim b As Integer = 20
        Dim total, total1 As Integer
        Console.WriteLine(" First Number is : {0}", a)
        Console.WriteLine(" Second Number is : {0}", b)
        total = SumOfTwo(a, b) 'call SumOfTwo() Function
        total1 = SubtractionOfTwo(a, b) 'call SubtractionOfTwo() Function
        Console.WriteLine(" Sum of two number is : {0}", total)
        Console.WriteLine(" Subtraction of two number is : {0}", total1)
        Console.WriteLine(" Press any key to exit...")
        Console.ReadKey()
    End Sub
End Module

Output:

In the above example, we have defined a SumOfTwo() and SubtractionOfTwo() function to add and subtract two predefined numbers. When the functions are called in the main() method, each function is executed and returns the sum and subtraction of two numbers, respectively.

Example: Write a program to reverse a number and check whether the given number is palindrome or not.

Palindrome.vb

Imports System
Module Palindrome
    ' Define a reverse() function 
    Function reverse(ByVal num As Integer) As Integer
        ' Define the local variable
        Dim remain As Integer
        Dim rev As Integer = 0
        While (num > 0)
            remain = num Mod 10
            rev = rev * 10 + remain
            num = num / 10
        End While
        Return rev
    End Function
    Sub Main()
        ' Define the local variable as integer
        Dim n, num2 As Integer
        Console.WriteLine(" Enter a number")
        n = Console.ReadLine() 'Accept the number
        num2 = reverse(n) ' call a function
        Console.WriteLine(" Reverse of {0} is {1}", n, num2)

        If (n = reverse(n)) Then
            Console.WriteLine(" Number is a Palindrome")
        Else
            Console.WriteLine(" Number is not a Palindrome")
        End If
        Console.WriteLine("Press any key to exit...")
        Console.ReadKey()
    End Sub
End Module

Output:

Recursive Function

When a function calls itself until the defined condition is satisfied, it is known as a recursive function. A recursive function is useful for solving many mathematical tasks such as generating the Fibonacci series, the factorial of a number, etc.

Let's create a program to calculate the factorial of a number using the recursive function.

Factorial_function.vb

Imports System
Module Factorial_function
    ' Create a Fact() function
    Function Fact(ByVal num As Integer) As Integer
        If (num = 0) Then
            Return 0
        ElseIf (num = 1) Then
            Return 1
        Else
            Return num * Fact(num - 1)
        End If
    End Function
    Sub Main()
        ' Define the local variable as integer
        Dim n, f As Integer
        Console.WriteLine(" Enter the number you want to calculate factorial")
        n = Console.ReadLine() 'Accept a number
        f = Fact(n) 'call Fact() function
        Console.WriteLine(" Factorial is : {0}", f)
        Console.WriteLine(" Press any key to exit...")
        Console.ReadKey()
    End Sub
End Module

Output:

Passing Array as a Parameter

Let's create a program that parses an array as a pass parameters in a function.

Array_Parameter.vb

Imports System
Module array_Parameter
    Function AddPara(ByVal Arr As Integer(), ByVal size As Integer) As Double
        'Declare a local variable.

        Dim i As Integer
        Dim avg As Double
        Dim Sum As Integer = 0

        For I = 0 To size - 1
            Sum = Sum + Arr(i)
        Next
        avg = Sum / size
        Return avg
    End Function
    Sub Main()
        Dim arrays As Integer() = {50, 10, 20, 5, 4, 25}
        Dim getAvg As Double
        getAvg = AddPara(arrays, 6)
        Console.WriteLine("Average sum of array element is {0}", getAvg)
        Console.WriteLine(" Press any key to exit...")
        Console.ReadKey()
    End Sub
End Module

Output: