A procedure is a group of statements that together perform a task, when called. After the procedure is executed, the control returns to the statement calling the procedure. VB.Net has two types of procedures:
Functions
Sub procedures or Subs
Functions return a value, where Subs do not return a value.
Defining a Function
The Function statement is used to declare the name, parameter and the body of a function. The syntax for the Function statement is:
[Modifiers] Function FunctionName [(ParameterList)] As ReturnType
[Statements]
End Function
Where,
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Modifiers: specifiy the access level of the function; possible values are: Public, Private, Protected, Friend, Protected Friend and information regarding overloading, overriding, sharing, and shadowing.
FunctionName: indicates the name of the function
ParameterList: specifies the list of the parameters
ReturnType: specifies the data type of the variable the function returns
Example
Following code snippet shows a function FindMax that takes two integer values and returns the larger of the two.
Function FindMax(ByVal num1 As Integer, ByVal num2 As Integer) As Integer
' local variable declaration */
Dim result As Integer
If (num1 > num2) Then
result = num1
Else
result = num2
End If
FindMax = result
End Function
Function Returning a Value
In VB.Net a function can return a value to the calling code in two ways:
The following example demonstrates using the FindMax function:
Module myfunctions
Function FindMax(ByVal num1 As Integer, ByVal num2 As Integer) As Integer
' local variable declaration */
Dim result As Integer
If (num1 > num2) Then
result = num1
Else
result = num2
End If
FindMax = result
End Function
Sub Main()
Dim a As Integer = 100
Dim b As Integer = 200
Dim res As Integer
res = FindMax(a, b)
Console.WriteLine("Max value is : {0}", res)
Console.ReadLine()
End Sub
End Module
When the above code is compiled and executed, it produces following result:
Max value is : 200
Recursive Function
A function can call itself. This is known as recursion. Following is an example that calculates factorial for a given number using a recursive function:
Module myfunctions
Function factorial(ByVal num As Integer) As Integer
' local variable declaration */
Dim result As Integer
If (num = 1) Then
Return 1
Else
result = factorial(num - 1) * num
Return result
End If
End Function
Sub Main()
'calling the factorial method
Console.WriteLine("Factorial of 6 is : {0}", factorial(6))
Console.WriteLine("Factorial of 7 is : {0}", factorial(7))
Console.WriteLine("Factorial of 8 is : {0}", factorial(8))
Console.ReadLine()
End Sub
End Module
When the above code is compiled and executed, it produces following result:
Factorial of 6 is: 720
Factorial of 7 is: 5040
Factorial of 8 is: 40320
Param Arrays
At times, while declaring a function or sub procedure you are not sure of the number of arguments passed as a parameter.
VB.Net param arrays (or parameter arrays) come into help at these times.
The following example demonstrates this:
Module myparamfunc
Function AddElements(ParamArray arr As Integer()) As Integer
Dim sum As Integer = 0
Dim i As Integer = 0
For Each i In arr
sum += i
Next i
Return sum
End Function
Sub Main()
Dim sum As Integer
sum = AddElements(512, 720, 250, 567, 889)
Console.WriteLine("The sum is: {0}", sum)
Console.ReadLine()
End Sub
End Module
When the above code is compiled and executed, it produces following result:
The sum is: 2938
Passing Arrays as Function Arguments
You can pass an array as a function argument in VB.Net. The following example demonstrates this:
Module arrayParameter
Function getAverage(ByVal arr As Integer(), ByVal size As Integer) As Double
'local variables
Dim i As Integer
Dim avg As Double
Dim sum As Integer = 0
For i = 0 To size - 1
sum += arr(i)
Next i
avg = sum / size
Return avg
End Function
Sub Main()
' an int array with 5 elements '
Dim balance As Integer() = {1000, 2, 3, 17, 50}
Dim avg As Double
'pass pointer to the array as an argument
avg = getAverage(balance, 5)
' output the returned value '
Console.WriteLine("Average value is: {0} ", avg)
Console.ReadLine()
End Sub
End Module
When the above code is compiled and executed, it produces following result:
Average value is: 214.4
