VB.NET Sub

A Sub procedure is a separate set of codes that are used in VB.NET programming to execute a specific task, and it does not return any values. The Sub procedure is enclosed by the Sub and End Sub statement. The Sub procedure is similar to the function procedure for executing a specific task except that it does not return any value, while the function procedure returns a value.

Defining the Sub procedure

Following is the syntax of the Sub procedure:

[Access_Specifier ] Sub Sub_name [ (parameterList) ] 
[ Block of Statement to be executed ]
End Sub

Where,

Access_Specifier: It defines the access level of the procedure such as public, private or friend, Protected, etc. and information about the overloading, overriding, shadowing to access the method.
Sub_name: The Sub_name indicates the name of the Sub that should be unique.
ParameterList: It defines the list of the parameters to send or retrieve data from a method.

The following are the different ways to define the types of Sub method.

Public Sub getDetails()
' Statement to be executed
End Sub

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

Public Function GetData1( ByRef username As String, ByRef userId As Integer)
' Statement to be executed
End Sub

Example: Write a simple program to pass the empty, a single or double parameter of Sub procedure in the VB.NET.

Sub_Program.vb

Module Sub_Program
    Sub sample()
        Console.WriteLine("Welcome to JavaTpoint")
    End Sub

    Sub circle(ByVal r As Integer)
        Dim Area As Integer
        Const PI = 3.14
        Area = PI * r * r
        Console.WriteLine(" Area Of circle is : {0}", Area)
    End Sub

    ' Create the SumOfTwo() Function and pass the parameters.
    Sub SumOfTwo(ByVal n1 As Integer, ByVal n2 As Integer)
        ' Define the local variable.
        Dim sum As Integer = 0
        sum = n1 + n2
        Console.WriteLine(" Sum of two number is : {0}", sum)
    End Sub

    Sub SubtractionOfTwo(ByVal n1 As Integer, ByVal n2 As Integer)
        ' Define the local variable.
        Dim subtract As Integer
        subtract = n1 - n2
        Console.WriteLine(" Subtraction of two number is : {0}", subtract)
    End Sub

    Sub MultiplicationOfTwo(ByVal n1 As Integer, ByVal n2 As Integer)
        ' Define the local variable.
        Dim multiply As Integer
        multiply = n1 * n2
        Console.WriteLine(" Multiplication of two number is : {0}", multiply)
    End Sub

    Sub Main()
        ' Define the local variable a, b and rad.
        Dim a, b, rad As Integer
        sample() ' call sample() procedure
        Console.WriteLine(" Please enter the First Number : ")
        a = Console.ReadLine()
        Console.WriteLine(" Second Number is : ")
        b = Console.ReadLine()

        SumOfTwo(a, b) 'call SumOfTwo() Function
        SubtractionOfTwo(a, b) 'call SubtractionOfTwo() Function
        MultiplicationOfTwo(a, b) 'call MultiplicationOfTwo() Function

        Console.WriteLine(" Enter the radius of circle : ")
        rad = Console.ReadLine()
        circle(rad)
        Console.WriteLine(" Press any key to exit...")
        Console.ReadKey()
    End Sub
End Module

Output:

In the VB.NET programming language, we can pass parameters in two different ways:

Passing parameter by Value
Passing parameter by Reference

Passing parameter by Value

In the VB.NET, passing parameter by value is the default mechanism to pass a value in the Sub method. When the method is called, it simply copies the actual value of an argument into the formal method of Sub procedure for creating a new storage location for each parameter. Therefore, the changes made to the main function's actual parameter that do not affect the Sub procedure's formal argument.

Syntax:

Sub Sub_method( ByVal parameter_name As datatype )
[ Statement to be executed]
End Sub

In the above syntax, the ByVal is used to declare parameters in a Sub procedure.

Let's create a program to understand the concept of passing parameter by value.

Passing_value.vb

Imports System
Module Passing_value
    Sub Main()
        ' declaration of local variable
        Dim num1, num2 As Integer
        Console.WriteLine(" Enter the First number")
        num1 = Console.ReadLine()
        Console.WriteLine(" Enter the Second number")
        num2 = Console.ReadLine()
        Console.WriteLine(" Before swapping the value of 'num1' is {0}", num1)
        Console.WriteLine(" Before swapping the value of 'num2' is {0}", num2)
        Console.WriteLine()

        'Call a function to pass the parameter for swapping the numbers.
        swap_value(num1, num2)
        Console.WriteLine(" After swapping the value of 'num1' is {0}", num1)
        Console.WriteLine(" After swapping the value of 'num2' is {0}", num2)
        Console.WriteLine(" Press any key to exit...")
        Console.ReadKey()
    End Sub

    ' Create a swap_value() method
    Sub swap_value(ByVal a As Integer, ByVal b As Integer)
        ' Declare a temp variable
        Dim temp As Integer
        temp = a ' save the value of a to temp
        b = a   ' put the value of b into a
        b = temp ' put the value of temp into b
    End Sub
End Module

Output:

Passing parameter by Reference

A Reference parameter is a reference of a variable in the memory location. The reference parameter is used to pass a reference of a variable with ByRef in the Sub procedure. When we pass a reference parameter, it does not create a new storage location for the sub method's formal parameter. Furthermore, the reference parameters represent the same memory location as the actual parameters supplied to the method. So, when we changed the value of the formal parameter, the actual parameter value is automatically changed in the memory.

The syntax for the passing parameter by Reference:

Sub Sub_method( ByRef parameter_name, ByRef Parameter_name2 )
[ Statement to be executed]
End Sub

In the above syntax, the ByRef keyword is used to pass the Sub procedure's reference parameters.

Let's create a program to swap the values of two variables using the ByRef keyword.

Passing_ByRef.vb

Imports System
Module Passing_ByRef
    Sub Main()
        ' declaration of local variable
        Dim num1, num2 As Integer
        Console.WriteLine(" Enter the First number")
        num1 = Console.ReadLine()
        Console.WriteLine(" Enter the Second number")
        num2 = Console.ReadLine()
        Console.WriteLine(" Before swapping the value of 'num1' is {0}", num1)
        Console.WriteLine(" Before swapping the value of 'num2' is {0}", num2)
        Console.WriteLine()

        'Call a function to pass the parameter for swapping the numbers.
        swap_Ref(num1, num2)
        Console.WriteLine(" After swapping the value of 'num1' is {0}", num1)
        Console.WriteLine(" After swapping the value of 'num2' is {0}", num2)
        Console.WriteLine(" Press any key to exit...")
        Console.ReadKey()
    End Sub

    ' Create a swap_Ref() method
    Sub swap_Ref(ByRef a As Integer, ByRef b As Integer)
        ' Declare a temp variable
        Dim temp As Integer
        temp = a ' save the value of a to temp
        a = b   ' put the value of b into a
        b = temp ' put the value of temp into b
    End Sub
End Module

Output: