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A function is a block of statements that performs a specific task.
A large program in c can be divided to many subprogram
The subprogram posses a self contain components and have well define
purpose. The subprogram is called as a function
Basically a job of function is to do something
C program contain at least one function which is main().
Classification of Function
Library
function
User define
function
- main() -printf()
-scanf()
-pow()
-ceil()

It is much easier to write a structured program where a large program can be divided into a
smaller, simpler task.
Allowing the code to be called many times
Easier to read and update
It is easier to debug a structured program where there error is easy to find and fix

C program doesn't execute the statement in function until the function is called.
When function is called the program can send the function information in the form
of one or more argument.
When the function is used it is referred to as the called function
Functions often use data that is passed to them from the calling function
Data is passed from the calling function to a called function by specifying the
variables in a argument list.
Argument list cannot be used to send data. Its only copy data/value/variable that
pass
from the calling function.
The called function then performs its operation using the copies.

Provides the compiler with the description of functions that will be used later
in the
program
Its define the function before it been used/called
Function prototypes need to be written at the beginning of the program.
The function prototype must have :
A return type indicating the variable that the function will be return
Syntax for Function Prototype
return-type function_name( arg-type name-1,...,arg-type name-n);
Function Prototype Examples
 double squared( double number );
 void print_report( int report_number );

It is the actual function that contains the code that will be execute.
Should be identical to the function prototype.
Syntax of Function Definition
return-type function_name( arg-type name-1,...,arg-type name-n) ---- Function
header
{
declarations;
statements;
return(expressio
n);
}
Function
Body

Function Definition Examples
float conversion (float celsius)
{
float fahrenheit;
fahrenheit =
celcius*33.8 return
fahrenheit;
}
The function name‟s isconversion
This function accepts arguments celcius of the type float. The function return a float
value.
So, when this function is called in the program, it will perform its task which is to
convert fahrenheit by multiply celcius with 33.8 and return the result of the
summation.
Note that if the function is returning a value, it needs to use the keyword return.

Can be any of C‟sdata type:
char
int
float
long………
Examples:
/* Returns a type int. */int func1(...)
float
func2(...)
void
func3(...)
/* Returns a type float.
*/
/* Returns nothing. */

`1: #include <stdio.h>
2:
3: long cube(long
x); 4:
5: long input, answer;
6:
7: int main( void )
8: {
9: printf(“Enter an integer value:
”); 10: scanf(“%d”,
&input);
11: answer = cube(input);
12: printf(“nThe cube of %ld is %ld.n”, input,
answer); 13:
14: return 0;15: }
16:
17: long cube(long x) //called
function 18:
{
x_cubed = x * x *
x; return
x_cubed;
19: long x_cubed;
20:
21:
22:
23: }
 Function names is cube
 Variable that are requires
is long
 The variable to be passed
on is X(has single
arguments)— value can
be passed to function so it
can perform the specific
task. It is called
Output
Enter an integer
value:4 The cube of 4
is 64.
Return datatype
Arguments/formalparameter
Actualparameters

• Write a program in C to find the square of any number using the function.
Test Data :
Input any number for square : 20
Expected Output :
The square of 20 is : 400.00
• Write a program in C to check a given number is even or odd using the function.
Test Data :
Input any number : 5
Expected Output :
The entered number is odd.

Function can be divided into 4 categories:
1. A function with no arguments and no return value
2. A function with no arguments and a return value
3. A function with an argument or arguments and returning no value
4. A function with arguments and returning a values

A function with no arguments and no return
valueCalled function does not have any arguments
Not able to get any value from the calling
function Not returning any value
There is no data transfer between the calling function and called
function.#include<stdio.h
>
#include<conio.
h> void
printline();
void main()
{
printf("Welcome to function in C");
printline();
printf("Function easy to
learn."); printline();
getch();
}
void printline()
{
int i;
printf("n");
for(i=0;i<30;i+
+)
{ printf("-"); }

A function with no arguments and a return
valueDoes not get any value from the calling
function
Can give a return value to calling program
#include
<stdio.h>
#include
<conio.h> int
send();
void main()
{
int z;
z=send(
);
printf("nYou entered :
%d.",z); getch();
}
int send()
{
int no1;
printf("Enter a no:
");
scanf("%d",&no1);
Enter a no: 46
You entered : 46.

A function with an argument or arguments and returning
no value
A function has argument/s
A calling function can pass values to function called , but calling function not
receive any value
Data is transferred from calling function to the called function but no
data is transferred from the called function to the calling function
Generally Output is printed in the Called function
A function that does not return any value cannot be used in an expression it
can be used only as independent statement.

#include<stdio.h>
#include<conio.h>
void add(int x, int
y);
void main()
{
add(30,15);
add(63,49);
add(952,321);
getch();
}
void add(int x, int y)
{
int result;
result =
x+y;
printf("Sum of %d and %d is
%d.nn",x,y,result);

A function with arguments and returning a
valuesArgument are passed by calling function to the called function
Called function return value to the calling function
Mostly used in programming because it can two way communication
Data returned by the function can be used later in our program for further
calculation.

Result 85.
Result 1273.
#include
<stdio.h>
#include
<conio.h> int
add(int x,int y);
void main()
{
int z;
z=add(952,321);
printf("Result %d.
nn",add(30,55)); printf("Result
%d.nn",z);
getch();
}
int add(int x,int y)
{
int result;
result = x +
Send 2 integer value x and y to
add()
Function add the two values and
send back the result to the calling
function
int is the return type of
function
Return statement is a keyword and
in bracket we can give values
which we want to return.

Variable that declared occupies a memory according to it size
It has address for the location so it can be referred later by CPU for
manipulation The „*‟and „&‟Operator
Int x=
10
x
10
7685
8
Memory location name
Value at memory
location Memory
location address
We can use the address which also point the same
value.

#include
<stdio.h>
#include
<conio.h>
void main()
{
int i=9;
printf("Value of i : %dn",i);
printf("Adress of i %dn",
&i);
getch();
}
& show the address of the
variable

#include
<stdio.h>
#include
<conio.h>
void main()
{
int i=9;
printf("Value of i : %dn",i);
printf("Address of i %dn", &i);
printf("Value at address of i: %d",
*(&i));
getch();
}
* Symbols called the value at the
address

#include
<stdio.h>
#include
<conio.h>
int Value (int x);
int Reference (int *x);
int main()
{
int Batu_Pahat =
2; int Langkawi =
2;
Value(Batu_Pahat);
Reference(&Langkawi
);
printf("Batu_Pahat is number
%dn",Batu_Pahat); printf("Langkawi is
number %d",Langkawi);
}
int Value(int x)
{
x = 1;
}
int Reference(int *x)
{
*x = 1;
}
Pass by reference
You pass the variable address
Give the function direct access to the
variable

#include
<stdio.h>
#include
<conio.h>
void callByValue(int, int);
void callByReference(int *, int *);
int main()
{
int x=10, y =20;
printf("Value of x = %d and y = %d.
n",x,y);
printf("nCAll By Value function
call...n"); callByValue(x,y);
printf("nValue of x = %d and y = %d.n",
x,y);
printf("nCAll By Reference function
call...n"); callByReference(&x,&y);
printf("Value of x = %d and y = %d.n",

void callByValue(int x, int y)
{
int temp;
temp=x;
x=y;
y=temp;
printf("nValue of x = %d and y = %d inside callByValue
function",x,y);
}
void callByReference(int *x, int *y)
{
int temp;
temp=*x
;
*x=*y;
*y=temp;
}

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