VB.Net - Sub Procedure (sub-program)

As we mentioned in the previous chapter, the Sub procedure is a process that does not return any values. W e've been using sub-process Main in all our examples. S o far, we've written console applications in these tutorials. W hen these applications start, control goes to the main sub-program, which in turn runs any other statements that make up the main body of the program.

Define sub-procedures

Sub statements are used to declare the name, parameters, and body of a sub-procedure. T he syntax of sub statements is:

[Modifiers] Sub SubName [(ParameterList)] 
    [Statements]
End Sub

• Modifiers modifier: specifies the level of access to the procedure; Possible values are: Public, Private, Protected, Friend, Protected Friend and information withing overloading, overriding, sharing, and shadowing
  

• SubName sub-name: Represents the child's name

• ParameterList Parameter List: A list of specified parameters

Example

The following example demonstrates a sub-process, CalculatePay, which accepts two parameter hours and salaries and shows the employee's total salary:

   Sub CalculatePay(ByRef hours As Double, ByRef wage As Decimal)
      'local variable declaration
      Dim pay As Double
      pay = hours * wage
      Console.WriteLine("Total Pay: {0:C}", pay)
   End Sub
   Sub Main()
      'calling the CalculatePay Sub Procedure
      CalculatePay(25, 10)
      CalculatePay(40, 20)
      CalculatePay(30, 27.5)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following results:

Total Pay: $250.00
Total Pay: $800.00
Total Pay: $825.00

Pass arguments by value

This is the default mechanism for passing parameters to methods. I n this mechanism, when a method is called, a new storage location is created for each value parameter. T he values of the actual parameters are copied into them. T herefore, changes made to the parameters in the method have no effect on the parameters.

In VB.Net, you can use the ByVal keyword to declare reference parameters. T he following example demonstrates this concept:

Module paramByval
   Sub swap(ByVal x As Integer, ByVal y As Integer)
      Dim temp As Integer
      temp = x ' save the value of x 
      x = y    ' put y into x 
      y = temp 'put temp into y 
   End Sub
   Sub Main()
      ' local variable definition 
      Dim a As Integer = 100
      Dim b As Integer = 200
      Console.WriteLine("Before swap, value of a : {0}", a)
      Console.WriteLine("Before swap, value of b : {0}", b)
      ' calling a function to swap the values '
      swap(a, b)
      Console.WriteLine("After swap, value of a : {0}", a)
      Console.WriteLine("After swap, value of b : {0}", b)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following results:

Before swap, value of a :100
Before swap, value of b :200
After swap, value of a :100
After swap, value of b :200

It indicates that although they have changed inside the function, there has been no change in the value.

Pass the parameter by reference

A reference argument is a reference to the memory location of a variable. W hen you pass parameters by reference, unlike value parameters, no new storage locations are created for those parameters. T he reference parameters represent the same memory location as the actual parameters provided to the method.

In VB.Net, you can use the ByRef keyword to declare reference parameters. T he following example demonstrates this:

Module paramByref
   Sub swap(ByRef x As Integer, ByRef y As Integer)
      Dim temp As Integer
      temp = x ' save the value of x 
      x = y    ' put y into x 
      y = temp 'put temp into y 
   End Sub
   Sub Main()
      ' local variable definition 
      Dim a As Integer = 100
      Dim b As Integer = 200
      Console.WriteLine("Before swap, value of a : {0}", a)
      Console.WriteLine("Before swap, value of b : {0}", b)
      ' calling a function to swap the values '
      swap(a, b)
      Console.WriteLine("After swap, value of a : {0}", a)
      Console.WriteLine("After swap, value of b : {0}", b)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following results:

Before swap, value of a : 100
Before swap, value of b : 200
After swap, value of a : 200
After swap, value of b : 100