Programming (OLD) - Procedures, Functions and Modules

 CBSE Class 12 Informatics Practices

Revision Notes
Chapter - 6
Procedures, Functions and Modules

Procedure: In computer programming, a procedure is a set of coded instructions that tell a computer how to run a program or calculation. Many different types of programming languages can be used to build a procedure. Depending on the programming language, a procedure may also be called a subroutine, subprogram or function.

Role of Procedure:
Increase Reusability - Using same code again and again.
Modularization - Means to divide a Big program into small modules.

Types of General Procedure:
1) Sub - A procedure performs a task and does not return a value.
Private/Public Sub Procedure - Name (parameter list)
Statements
End Sub
Eg: Write a VB Procedure that receives a number and check that it is even or odd.
Called Procedure:-
Sub checkEvenOdd (x as Integer)
If x mod 2 = 0 then
Print “Even No.”
Else
Print “Odd No.”
End if
End Sub
Calling Program:-
Private sub command1_click( )
Dim A as Integer
A = val(Inputbox(“Enter a No”))
Call checkEvenOdd (A)
End Sub

2) Function - 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, whereas Subs do not return a value. 
Eg: Write a VB Function that receives a number and Returns True if it is even otherwise False.
Called Function:
Function checkEvenOdd (x as Integer) As Boolean
If x mod 2 = 0 then
checkEvenOdd = TRUE
Else
checkEvenOdd = FALSE
End if
End Function
Calling program:
Private sub command1_click( )
Dim x as Boolean
Dim A as Integer
A = val (Inputbox (“Enter a No”))
x = checkEvenOdd (A)
If x = TRUE then
Msgbox “Even No.”
Else
Msgbox “Odd No.”
End If
End Sub

Call byVal and Call byRef:-
The call byVal method copies the values of actual parameter into the formal parameters, ie. The procedure creates its own copy of argument values and then uses them. Only a copy of a variable is passed to the called procedure and if the procedure changes the value, the changes affects only the copy and not reflected back to the original variable itself.
Sub DemoByValue (ByVal x as Intyege)
x = x + 10
Print x
End Sub
Private sub mainprg( )
Dim A as Integer
A = 10
Print A
Call DemoByValue( A)
Print A
End Sub
The O/P is:
10
20
10

The call byRef method does not creates its own copy of original values, rather it refers to the original values only by different names called reference, and thus the called procedure works with the original data and any changes in the values gets reflected to the data.
Sub DemoByReference (ByRef x as Integer)
x = x + 10
Print x
End Sub
Private sub mainprg( )
Dim A as Integer
A = 10
Print A
Call DemoByReference ( A)
Print A
End Sub
The O/P is:
10
20
20

Code Modules:- A module is a container in VB, that contain some variables, procedures and definition.
Three types of Modules are:
1) Form Module - Stores all the procedures and declarations pertaining to single form. Form modules are stored with .FRM extension. They can contain procedures that handle events, general procedures, and form-level declarations of variables, constants, types, and external procedures. 
2) Standard Module - Store general purpose code of the application, ie code and declaration that are not specific to a form. Standard modules are stored with .BAS extension. They can contain global (available to the whole application) or module-level declarations of variables, constants, types, external procedures, and global procedures. 
3) Class Module - It stores the blueprint for user created custom object. Class modules are stored with . CLS extension. You can write code in class modules to create new objects. These new objects can include your own customized properties and methods. 

Variables Used Within a Procedure

Procedure-level variables are recognized only in the procedure in which they're declared. These are also known as local variables. You declare them with the Dim or Static keywords. For example:

Dim intTemp As Integer

–or–

Static intPermanent As Integer

Variable Scope: - The part of a program within which a variable is accessible, is known as its scope.
Three Variable Scopes are:
1) Private Scope/ Local Scope - Variables declared within a procedure are in local scope.
2) Module Scope - Variables available for all the procedures within that module.
3) Public Scope / Global Scope - Variables declared with public statement and available to the application.

Variables Used Within a Module

Private intTemp As Integer

Static Variables: Local and Static variable differ by their life span. Static variables retain its value even after the procedure has finished executing.
Which variable is static in the following function?
Static function MyFunction ( )
Static X1 as Integer
Dim Y1 as Integer
End Function
Ans: - Both X1 and Y1 are static variables because a Static function makes all its local variables Static.