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Functions & Subroutines

Functions & Subroutines, What are they? What they do?

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AdamSpeight2008
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6 Apr, 2009 - 03:02 PM

Post #1

Subroutines & Functions

Subroutine

A subroutine is a code construct.
A code construct is a pattern of coding. Examples;- For Loops, Do Whiles Loops, Sub ... End Sub, Function .... End Function
A subroutine is a self contained section of code, that;-
Has Inputs: Possible
Has Output: Never

CODE

Private Sub PrintHelloWorld()
Console.WriteLine("Hello World")
End Sub

Where you put your code to handle a button click is particular type of subroutine called An Event Handler
Indicated by the Handles Button1.Click.

CODE

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

End Sub

Functions
A function is a self contained section of code, that;-
Has Inputs: Generally Yes
Has Output: Always

CODE

Function SquareOfNumber(ByVal x As Decimal) As Decimal
Return x * x
End Function

Subroutines & Functions may contain calls to other Functions and Subroutines.

CODE

Function Factorial(ByVal x As Decimal) As Decimal
  Dim f As Decimal = 1
  While x > 1
   f = f * x
   x -= 1
  End While
  Return f
End Function

Function FactorialSquared(ByVal x Decimal) As Decimal
Return SquareOfNumber(Factorial(x))
End Function

Thats the basics of Functions & Subroutines.

For the more the adventurous

Q. What all the arguments of the preceding Functions & Subroutines have in common?
A. All the arguments are preceded by a ByVal.

There are to basic types (the object type of the arguments excluded) of argument.

ByVal This a copy of the object passed in. You can do what you like to this and it won't change the original object passed in as the argument.
ByRef This a REFerence to the actual object. What you do to this affects the original object passed in as the argument.

A ByRef argument allows the programmer to get information out of a Subroutine, like a Function.

Example 1 (Trivial): Increase the value of two Doubles by 2.

CODE

Public Sub IncreaseBothBy2(ByRef A As Double,ByRef B As Double)
A+=2
B+=2
End Sub

Example 2: Clear the text of any textbox.

CODE

Sub ClearTextbox(ByRef Tb As Textbox)
Tb.Text=""
End Sub

I hope now you'll be a Function & Subroutine wielding Code-Ninja.

Edit: Mismatched tag
Edit: The 100th VB.net Tutorial on DiC

This post has been edited by AdamSpeight2008: 7 Apr, 2009 - 06:04 AM

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AdamSpeight2008
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7 Apr, 2009 - 11:03 AM

Post #2

Postscript

A Subroutine or Function that calls itself is called recursive. This process is call recursion, and you have to be careful.

CODE

Function Factorial(ByVal x As UInteger) As UInteger
Return x * Factorial(x-1)
End Function

Problem: The above function will continue to call itself, until it filled the stack and the crashes.
Solution: Add base conditions

CODE

Function Factorial(ByVal x As UInteger) As UInteger
' A base condition to end the recursion.
If x=0 Then Return 1
Return x * Factorial(x-1)
End Function