VB.NET Tutorials

Welcome to Dream.In.Code
	Become an Expert! Join 307,124 Programmers for FREE! Get instant access to thousands of experts, tutorials, code snippets, and more! There are 2,034 people online right now. Registration is fast and FREE... Join Now! Chat LIVE With a Expert

Functions & Subroutines

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

Options

AdamSpeight2008
Group Icon

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

Register to Make This Ad Go Away!

AdamSpeight2008
Group Icon

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