CHAPTER 6

FUNCTIONS
EC201- FUNDAMENTAL
PROGRAMMING

What is Function
 Block of code that performs a specific task.
 It has a name and it is reusable i.e. it can be executed
from as many different parts in a C Program as required.
Every function has a unique name. This name is used to
call function from “main()” function. A function can be
called from within another function.
 It also optionally returns a value to the calling program
 Performs a specific task. A task is a distinct job that your
program must perform as a part of its overall operation,
such as adding two or more integer, sorting an array into
numerical order, or calculating a cube root etc.

Sample Function Call
#include <stdio.h>
int main ( ) printf is the name of a predefined
{ function in the stdio library
printf (“Hello World!n”) ; this statement is
return 0 ; is known as a
} function call
this is a string we are passing
as an argument (parameter) to
the printf function

Function
• The ‘building blocks’ of a C program
▫ You’ve used predefined functions already:
 main()
 printf(), scanf(), pow()
▫ User-defined functions
 Your own code
 In combination with predefined functions

Sample User-Defined Function
#include <stdio.h>
void printMessage ( void ) ;
int main ( void )
{
printMessage ( ) ;
return 0 ;
}
void printMessage ( void )
{
printf (“A message for you:nn”) ;
printf (“Have a nice day!n”) ;
}

Examining printMessage
#include <stdio.h>
void printMessage ( void ) ; function prototype
int main ( void )
{
printMessage ( ) ; function call
return 0 ;
}
void printMessage ( void ) function header
{
printf (“A message for you:nn”) ; function
printf (“Have a nice day!n”) ; body
}
function definition

Program example: functions
#include<stdio.h>
kira(int t_semasa, int t_lahir);
main()
{
int t_semasa,t_lahir,u;
printf("Please enter your birth year:");
scanf("%d",&t_lahir);
printf("Please enter the current year:");
scanf("%d",&t_semasa);
u = kira(t_semasa,t_lahir);
printf("nYour age is: %d years oldnn",u);
return 0;
}
kira(int t_semasa, int t_lahir)
{
int umur;
umur = t_semasa-t_lahir;
return(umur);
}

Types of functions
Functions with no arguments and no return values.
Functions with arguments and no return values.
Functions with arguments and return values.
Functions that return multiple values.
Functions with no arguments and return values.

Functions with no arguments and no
return value
 A C function without any
arguments means you cannot
pass data (values like int, char
etc) to the called function.
 Similarly, function with no
return type does not pass back
data to the calling function. It is
one of the simplest types of
function in C.
 This type of function which
does not return any value
cannot be used in an expression
it can be used only as
independent statement.

Program example: Functions with no arguments and no return
value
#include<stdio.h>
cetak_line1();
cetak_line2();
main()
{
printf("Welcome to function in C");
cetak_line1();
printf("Function easy to learn.");
cetak_line1();
printf("Please make sure you really understand about this topic.");
cetak_line2();
return 0;
}
cetak_line1()
{
int i;
printf("n");
for(i=0;i<30;i++)
{
printf("-");
}
printf("n");
return 0;
}
cetak_line2()
{
printf("n--------------------------------------------------------");
return 0;
}

Functions with arguments and no
return value
 In our previous example what we have
noticed that “main()” function has no
control over the UDF “printfline()”, it
cannot control its output. Whenever
“main()” calls “printline()”, it simply
prints line every time. So the result
remains the same.
 A C function with arguments can
perform much better than previous
function type.
 This type of function can accept data
from calling function. In other words,
you send data to the called function
from calling function but you cannot
send result data back to the calling
function. Rather, it displays the result
on the terminal. But we can control the
output of function by providing various
values as arguments.

Program example: Functions with arguments and no return value
#include<stdio.h>
tambah(int x, int y);
main()
{
int x,y;
printf("Please enter a value x:");
scanf("%d",&x);
printf("Please enter a value y:");
scanf("%d",&y);
tambah(x,y);
return 0;
}
tambah(int x, int y)
{
int result;
result = x+y;
printf("Sum of %d and %d is %d.nn",x,y,result);
return 0;
}

Functions with arguments and return
value
 This type of function can send
arguments (data) from the
calling function to the called
function and wait for the result to
be returned back from the called
function back to the calling
function.
 This type of function is mostly
used in programming world
because it can do two way
communications; it can accept
data as arguments as well as can
send back data as return value.
 The data returned by the
function can be used later in our
program for further calculations.

Program example: Functions with arguments and return value
#include<stdio.h>
tambah(int x, int y);
main()
{
int x,y,z;
printf("Please enter a value x:");
scanf("%d",&x);
printf("Please enter a value y:");
scanf("%d",&y);
z = tambah(x,y);
printf("Result %d.nn",z);
return 0;
}
tambah(int x, int y)
{
int result;
result = x+y;
return(result);
}

Functions with no arguments but
returns value
 We may need a function which
does not take any argument but
only returns values to the
calling function then this type
of function is useful. The best
example of this type of function
is “getchar()” library function
which is declared in the header
file “stdio.h”. We can declare a
similar library function of own.

Program example: Functions with no arguments but returns value
#include<stdio.h>
send();
main()
{
int z;
z = send();
printf("nYou entered : %d.", z);
return 0;
}
send()
{
int no1;
printf("Enter a no : ");
scanf("%d",&no1);
return(no1);
}

Functions that return multiple values
• We have used arguments to send values to the
called function, in the same way we can also use
arguments to send back information to the
calling function.
• The arguments that are used to send back data
are called Output Parameters.
• Is a bit difficult for novice because this type of
function uses pointer.

Program example: Functions that return multiple values
#include<stdio.h>
calc(int x, int y, int *add, int *sub);
main()
{
int a,b,p,q;
printf("Please enter a value a:");
scanf("%d",&a);
printf("Please enter a value b:");
scanf("%d",&b);
calc(a,b,&p,&q);
printf("Sum = %d, Sub = %d",p,q);
return 0;
}
calc(int x, int y, int *add, int *sub)
{
*add = x+y;
*sub = x-y;
return (0);
}

CHAPTER 6

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