Global variable in QBASIC for class 10 and SEE
Introduction
For both newcomers and seasoned programmers, QBASIC has been a fundamental language in the world of programming. Global variables are one of the fundamental ideas that every QBASIC programmer needs to understand. Global variables will be thoroughly discussed in this article, along with their definition, usage, and importance in QBASIC programming.
What are Global variables?
Global variables are the variables which are
declared outside all procedures and main program. They are available to all the
blocks and modules. Thus, global variable can be used in whole program.
Why use Global Variables?
Global variables are useful for storing data that must be accessed from multiple parts of a program. For example, if you're writing a program to manage a database, you might declare a global variable to store the database file's name. This variable could then be accessed by any program subroutine or function that needs to read or write data to the database.
However, it is critical to use global variables with caution. If you use too many global variables, your program may become difficult to understand and maintain. Furthermore, if you are not cautious, global variables can cause errors if they are not used correctly.
Declaring Global Variables
In QBASIC, declaring a global variable is straightforward. You simply define it outside of any function or subroutine, at the beginning of your program.
In QBASIC global variables are declared by SHARED or
COMMON/DIM SHARED statements.
Example of Using a Global Variable in QBASIC
By using SHARED statement:
SHARED is a statement that allows accessing the
variables in every procedure declared at the main module without passing them
as parameters.
Syntax:
SHARED variable_list
Where,
Variable_list(s) is the variable to be accessed in
the program.
Example:
DECLARE SUB sum ()
DECLARE SUB diff ()
CLS
INPUT "Enter any two numbers"; a, b
CALL sum
CALL diff
END
SUB diff
SHARED a, b
su = a - b
PRINT "difference="; su
END SUB
SUB sum
SHARED a, b
s = a + b
PRINT "Sum="; s
END SUB
Note:
in above example, there is no parameter but h the variables “a”, and “b” are
shared in every module by SHARED statement.
By using COMMON SHARED statement:
COMMON is a non-executable statement that declares
global variables for sharing between modules.
Syntax:
COMMON SHARED variable_list
Example:
COMMON SHARED w$
DECLARE SUB rev ()
DECLARE SUB vowel ()
CLS
INPUT "Enter any word"; w$
CALL rev
CALL vowel
END
SUB rev
FOR x = LEN(w$) TO 1 STEP -1
m$ = m$ + MID$(w$, x, 1)
NEXT
PRINT m$
END SUB
SUB vowel
FOR x = 1 TO LEN(w$)
m$ = MID$(w$, x, 1)
SELECT CASE m$
CASE "a", "e", "i",
"o", "u"
PRINT m$
END SELECT
NEXT
END SUB
Note:
In above example, a COMMON statement establishes storage for variable in a
special area that allows them to be shared between modulus. The variable “w$”
of main module can shared in both sub modules “rev” and “vowel”
By using DIM SHARED statement:
This statement makes the variable accessible to all
the modules. It appears in the main program.
Syntax:
DIM SHARED variable(subscript)
Example:
WAP to input any five numbers and display them with
their sum.
DIM SHARED num(5)
DECLARE SUB add ()
CLS
FOR x = 1 TO 5
INPUT "enter number"; num(x)
NEXT
CALL add
END
SUB add
FOR x = 1 TO 5
PRINT num(x)
s = s + num(x)
NEXT
PRINT "sum="; s
END SUB
Conclusion:
Global variables in QBASIC are useful for storing data that must be accessed from multiple parts of a program. However, global variables must be used with caution because they can make your program difficult to understand and maintain.
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