Understanding SUB Procedures in QBASIC: A Complete Guide for Class 10 and SEE
Introduction
What are the SUB Procedures in QBASIC?
Features of SUB procedure:
i) It does not return any value
ii) Sub procedure name can't have a type of declaration characters
iii) Sub procedure name can't be used as a variable
iv) Sub procedure is called by CALL statement.
v) Arguments can be passed to the subprogram by reference and by value method
There are two types of
procedures used in QBASIC. They are:
i) SUB procedure
ii) FUNCTION procedure
Difference between Sub
procedure and Function procedure:
|
Sub procedure |
Function procedure |
|
Sub
procedure does not return a value in main module |
Function
procedure returns a single value in main module. |
|
It
can be called by CALL statement. |
It
can be called by expression or PRINT statement. |
|
The
program code placed between SUB and END SUB statement. |
The
program code placed between FUNCTION and END FUNCTION statement. |
SUB Procedure:
A sub procedure is a subroutine which is a block of statements to
carry out a well defined task. A sub procedure does not return a value. Once a
sub procedure defined, it can be called from the main module at any time. The
block statements are written in sub procedure using SUB…..ENDSUB statement
a) Declaring a Procedure
Before using any procedure in the QBASIC program, it must be
declared first. The declaration of the procedure requires procedure name with
the list of variable or constant to be passed to the procedure for processing.
A procedure in QBASIC is declared using DECLARE statement. If you forget
DECLARE the DECLARE statement to declare the procedure, QBASIC automatically
inserts the DECLARE statement before the procedure name. The DECLARE statement
consists of a procedure name along with a list of variables called arguments to
be passed to the procedure. The DECLARE statement verifies the number of
parameters and its types used in the procedure.
Syntax:
DECLARE SUB procedure_name [(parameter list)]
Where,
Procedure_name is the name of the SUB procedure. The name
is valid QBASIC identifier an can be maximum of 40 characters.
Parameter list are the list of variables that are used in procedure.
Example:
DECLARE SUB sum(x,y)
Above example declares
the sub-procedure sum with two parameters x and y. x and y are
numeric variables.
b) Defining a SUB procedure
After declaration of the
procedure in the main module, it is necessary to define the procedure. SUB…….END
SUB is a statement used to define sub procedure in the program. The procedure
is define as same as the procedure is declared in the main program. The number
of parameter list must match the number while defining the sub procedure.
When you type SUB keyword with name of the sub procedure, the QBASIC opens a new editing window with the procedure definition statement such as SUB……END SUB.
After saving the program
you can see the two names below the menu bar. i.e.
i) Program
name
and ii) Procedure
name
Note: To
return the main module press F2 key and vice versa for sub module
also.
After Pressing F2 key you can see the following
dialog box:
Now you can select the
desired module from the above dialog box and press the enter key to switch on
the module.
Syntax:
SUB sub_name[(parameter_lists)]
[statement
blocks]
END SUB
Where,
Sub_name is the name of the sub procedure. The name
can be written in the same way as variable name is written.
Parameter-lists are the list of variables which hold the
referenced values passed from the main module in the form of arguments
Statement
blocks contains valid QBASIC
statements.
Example:
SUB sum(x,y)
INPUT
“Enter any two numbers”;x,y
LET
s= x+y
PRINT
“SUM=”;s
END SUB
In above example sum is
the procedure name. The sub procedure sum contains two parameters a and b.
c) Calling a sub procedure:
Once the procedure is defined in the program, it can be called
anywhere in the program at any time. CALL statement is used to call a sub
procedure. When the sub procedure is called using CALL statement, after the sub
procedure the control of the program goes to CALL statement in the calling
procedure.
Syntax:
CALL sub_name[(argument_lists)]
Where,
CALL is the keyword used to call the sub
procedure
Sub_name is the name of the sub procedure to be
called.
Argument_list are the list of variables or constant
passed to the sub procedure for processing. The comma(,) is used to separated arguments.
Example:
CALL sum(a,b)
In above example, “sum”
is the sub procedure name that is to be called and “a” and “b” are arguments to
be passed to the subprogram.
Example:
WAP to input any two numbers in main module and display the
average of given two numbers in sub module.
Note: In above program, the user supplies two different numbers, which are stored by the variables “a” and “b”. CALL statement is used to connect main module to sub module and ass the value of a and b of main module to sub module. The average of two numbers calculated in sub module and result is stored in variable "av" and display it in sub module only.
Arguments and Parameters:
In a modular programming, there should be
exchange of values between main module and sub modules. It is necessary to pass
the data from main module to sub modules for processing. For the same,
arguments and parameters are used.
Parameters:
Parameters are the variables which accept data passed to them. When we define a
sub procedure, you specify a parameter list in parentheses immediately
following the procedure name. We can indicate that a parameter is optional. It
means that the calling code does not have to pass a value for it.
The consonant and variable enclosed in parenthesis of procedure
call statement and that are supplied to a procedure are known as arguments. Arguments are also known as actual parameters. The arguments are used to pass the values
to the procedure. Arguments are the constant values.
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