3.1 Modular Programming - SEE COMPUTER SCIENCE 2080

 3.1 Modular Programming

 

Modular programming
Modular programming is a technique used to divide our program into many small logical, manageable and functional modules or blocks.

 

Advantages of modular programming

l Many programmers can write different program modules independently.

l The debugging of the program becomes easier and faster.

l The same procedure can be used in different places, which reduces the program codes.

l It improves the readability of a program.

l It is easy to design code.

 

Types of  Procedure in Modular Programming

a) Sub-procedure

b) Function-procedure

 

Main Module - The main part of the program inside which several submodules are created.

 

Sub-Program - A group of statements written in a separate module to perform one or more tasks

 

Sub module / Procedure
Module is a block of statement that solves a particular problem.

SUB procedure
A sub-procedure is a small manageable and functional part of a program that performs specific tasks and does not return any value to the calling module.  

A CALL statement is used to call the sub procedure in a program.

SUB-procedure’s name does not accept data type symbol because it does not need to return a value.

Passing arguments by value (Call by value)

Call by value is a method of calling a procedure in which actual data are passed to the calling procedure module. It is done by enclosing each parameter by a separate parenthesis ( ).

 

Passing arguments by reference (Call by Reference)

Call by reference is a method of calling a procedure in which the reference (address) of parameters are passed to the calling procedure module instead of actual value. By default, the parameters are passed using call by reference method.

 

Formal parameters

Formal parameters are variables which are used to specify or declare types of data to be passed to the procedures either sub or function. A formal parameter is always variable(s).

 

Actual or Real parameters
Actual or Real parameters are arguments which are used to pass real value or data to the procedure.

Actual parameters may be variables or constant values or can also be in the form of expression.

 

Local variable

A variable which is defined in a module and is not accessible to any other modules is known as local variable

It is only accessible to the module where it is defined.

Value of local variable is destroyed when execution of module is over.

 

Global variable

A variable in main module which can be accessed from any module or procedure of a program is known as a global variable.

Variable can be made global declaring them with DIM SHARED or COMMON SHARED or SHARED statement.

 

 

FUNCTION procedure

A function-procedure is a small manageable and functional part of a program that performs specific tasks and returns a value to the calling module.  

FUNCTION-procedure is called by statement and expression method.

FUNCTION-procedure’s name accepts data type symbols such as $, %, !, #, &, etc. and it depends on the type of value to be returned. E.g.: FUNCTION REV$ returns string.

String function [SEE 2074 U]

String function is used with string it returns string value.

 

Numeric function [SEE 2074 U]

Numeric function is used with number it returns numeric value.

 

Library functions [SQE 2074K]
Library functions are built-in or readymade functions provided by QBASIC. E.g. MID$( ), LEN( ), SQR( ) etc.

User defined function
Function which is defined by the user according to the need is called user defined function.

 

 

CALL statement [SLC 2071] [PMT 2075K]
The function of CALL statement is to transfer control to another sub procedure from main module.

 

DECLARE statement
The function of DECLARE statement is to declare procedure such as FUNCTION or SUB in modular programming.

 

DIM SHARED / COMMON SHARED statement - to declare global variables in main module.

SHARED - to declare global variables in sub module