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Meaning : The process of
developing program by dividing it into two or more
manageable/functional parts ie; main
module and sub module, is called modular programming.
Main module: It the upper
level part of modular programming which controls all the sub program. Mainly it
is a data entry section for sub programs.
*Sub module/Procedure: It is a small program written under main
module, which process the data and returns the output. There may be one or more
sub modules under a main module. There are two types of sub programs viz;
i. SUB …END SUB
ii. FUNCTION…..END FUNCTION
Advantages of modular
programming:
·
it is easy and efficient to handle large project
·
Debugging is easier.
·
It reduces the task of repeated coding, since
same module can be used in different places.
a. Parameter: It the list
of variables or array name which are passed to the procedure formally, while
declaring the function or sub procedure. It may be null.
b. Arguments : It
is the list of variables, array name or
constant which are actually passed to the procedures at the time of calling
function. It should not be null. It is also called real or actual parameter.
c. Global variable : The
variable declared outside the modules is called global variable. It can be
accessed from both main module and sub module in the program. Generally,
variable declared inside parameter, with Dim shared and Common shared are
global variables.
d. Local variable: The variable which is restricted only inside
a particular module is called local variable. By default, the entire variable
is local in modular programming.
a. CALL :
This
statement is used to transfer the control between main module and sub
procedure. Without this statement, a program does not return the output.
FUNCTION…. END FUNCTION: It
is a user defined function, which accepts data, processes them and returns a
value of specific type. Function… End Function marks the beginning and ending
of Function procedure.
Features:
·
It returns the specific type of value.
·
It is recursive.
Types of function :
a)
User defined function: The function defined by the user in order
to return a particle type of value in the program is called user defined
function. Eg. Function …End Function and
Def… Fn. It can be called in the different sections within the same
program
b)
Library function : The functions which are stored in Qbasic
program is called library function. It is also known as inbuilt function. It
can be called in any programs. For ex. LEN(), INT(), etc.
Calling a Function : To
execute the function by passing argument for specific data value is called invoking or calling a function. It
can be called by the following ways :
·
Variable method (Expression method), eg. V= sum(a,b)
·
Print method(
statement method) , eg: print sum(a,b)
Common Shared : This statement is used to make the variable
accessible in both main module and sub module. It makes the variable global. It
is declared in main module.
Syntax : CCOMMON [ SHARED] VARIABLE
Eg. Common shared n,…
Dim Shared : It makes the variable accessible by sharing it in both
main module and sub module. It is also declared in main module.
Syntax: DIM SHARD VARIBLE(SIZE)as type
Eg: Dim shared P(10) as integer
Passing Arguments to procedures: When a procedure is called, the calling
statements pass the value to the procedure via arguments. There are two methods
of passing arguments. They are;
*By value : In this method,
the values passed to the procedure, does not modify its original value in
calling procedure. It is done by enclosing the argument in parenthesis.
Eg: Call Total( x,(y)); here ‘y’
argument is passed by value.
* By reference: In this method, the value is passed from parameters are
copied to the procedure so that any changes in called procedure will affect the
value in calling procedure. By default, all arguments are passed by reference
in modular programming.
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