CBSE Class 12 Informatics Practices Procedures Functions And Modules Notes

Procedures, Functions and Modules

It’s a named unit of a group of program statement that performs a well defined task. This unit can be called from the calling program.

Role of Procedure:

Increase Reusability – Using same code again and again.

Modularization – Means to divide a Big program into small modules.

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 - A procedure performs a task and returns a value.

Private/Public Function Function-Name( parameter list)

Statements

End Function

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 

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 thedata.

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.

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.

3) Class Module - It stores the blueprint for user created custom object. Class modules are stored with .CLS extension.

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.

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.

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