Functions:
To develop a complex and big application, the total
application has to divide into small and easily manageable parts called
modules.
A module is a part or unit of total application.
In C language a module is defined using function.
C language supports modularity using functions so is called
modular programming language.
Definition:
Function is a self-contained block of code that performs a
particular task. It is capable to communicate with other units of application.
Advantages:
A complex application can be divided into number of simple
and easily manageable parts called functions.
It is easy to develop, test and debug a small function.
It improves the maintainability of application because a
problem (bug) in a function can be easily detected and modified.
It improves the reusability because the same function can be
reused in different places.
It reduces the application development time because multiple
modules can be developed at a time and then integrated as a single application.
It reduces the required memory to run the application.
Foundation to functions: (7 steps to functions)
The following 7 points must be kept in mind while working
with functions.
Point 1.
Undefined variable can’t be used with in a function.
Example:
#include<stdio.h>
void main()
{
int a,b;
clrscr();
a=20;
b=25;
c=a+b;
printf("Sum of two numbers %d",c);
getch();
}
Output:
Error: Undefined symbol "c" in function main()
Example explained:
Variable "c" is not declared with in main() which
results error.
Point 2. Multiple
variables can’t be declared with the same name with in a function.
Example:
#include<stdio.h>
void main()
{
int x=25;
float x=12.25;
clrscr();
printf("x=%d",x);
printf("\nx=%f",x);
getch();
}
Output:
Error: Re declaration of "x" in function main.
Example explained:
Here "x" is declared for two times with in a
single function main() which results error.
Point 3. If a
variable is not assigned with any value then it is initialized with an unknown
value called garbage value.
Example:
#include<stdio.h>
void main()
{
int x;
clrscr();
printf("%d",x);
getch();
}
Output:
26500
Example explained:
It is garbage value differs from computer to computer and
execution to execution.
Point 4. A
function is a self-contained block of code that performs a particular task. It
has a name which must be a valid identifier.
A C program may have any number of functions but defining of
main() function is mandatory because execution of any C program starts and
completes from the main()
Functions other than the main() are called sub functions.
Sub functions are not executed unless we call them from the
main() directly or indirectly.
Example1:
#include<stdio.h>
main()
{
clrscr();
printf("Hello world");
getch();
}
first()
{
printf("\nNice World");
}
Output:
Hello world
Example explained:
The function first() is not executed because it is not
called from the main().
Example2:
Output:
One
Three
Two
Example explained:
The function first() is called from the main.
Example3:
Output:
One
Three
Five
Four
Two
Example explained:
Function first() is called directly from the main()
Function second() is called from the main() indirectly that
is through the first()
Example4:
#include<stdio.h>
main()
{
int i;
clrscr();
for(i=1;i<=5;i++)
hello();
getch();
}
hello()
{
printf("\nHello World");
}
Output:
Hello World
Hello World
Hello World
Hello World
Hello World
Example explained:
The function hello() is called for
5 times.
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