1. !!!!
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Function
Function is self-contained block of program that perform specific
task and return certain values.
Syntax: <return type><function name> (argument list);
- Return type is either void or int types
Every “C” program start with main () function which is user defined
functions.
- C language supports two types of functions.
- I) Library function
- II) User defined functions
Library Function: these are pre-defined functions in different
header file.
e.g: printf (),scanf(),gets(),sqrt(),pow() etc.
e.g:
#include<stdio.h>
#include<math.h>
Void main ()
{
int no, r;
printf (“Enter a number”);
scanf (“%d”,&no);
r=sqrt(no);
printf(“%d”,r);
}
User defined function:
They are defined by the user according user requirement. A user
defined function has three things.
i) Function prototype
ii) Function call
iii) Function definition

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Why use function: if we want to perform a task repeatedly then it
is not necessary to re-write the particular block of the program
again and again.
-Shift the particular block of statement in a user defined
function. the function defined can be used for any number of times
to perform the task.
- Use the function can be reduced to smaller one.
- It is easy to debug and find out the error.
- It also increases readability.
How it works: whenever a function is called control passes to the
called function and working of the calling function is stopped.
- When the execution of function is completed, control returns
to the calling function and execute the next statement.
- The value of actual argument passed by the calling function
and received by the formal argument of the called function.
The no of actual argument and formal argument are same.
- The function operates on formal argument and sends back the
result to the calling functions, the return () statement
performs this task.
Syntax to Declare the Calling Function:
<return type> <function name> (argument list with its data type);
Argumnent –declaration;
{
Statment1;
Statment2;
---------------
----------------
Return(values);
}
Actual argument: the argument calling function are actual
argument.

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Formal argument: the argument of called function is formal
argument.
Argument List: the argument list means various names enclosed
with in parenthesis. They must separated by comma.
Function Prototype:
- By default the function can pass integer type of data and
return integer type.
- Other than type of data, the function cannot pass and return.
In such cases we declare the function. Such definition of the
function is known as function prototype.
- The prototype of these function are given in header file. Those
we including using # include directives.
- In c while defining is defined function it must declare the
prototype.
- A prototype declaration consist of function return type ,name,
and arguments list.
- When programmers define the function of the function is same
as prototype declaration.
- If the programmer makes do any mistake, the compiler shows
the error message. The function prototype statement always
ends with semicolon.
Syntax:
Void main ()
{
Variable declaration/function declaration;
Value initialization;
Calling function
Printing result;
}
Function definition/return type function name (argument list)

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{
Formal argument declaration;
Operation;
Return result;
}
Function declaration is four types:
1) Function with return type with arguments.
2) Function without return type with arguments
3) Function with return type without arguments
4) Function without return type without arguments.
Example: W.A.P add two numbers.
1) Function with return type with arguments.
Void main()
{
Int add(int,int);
Int a,b,c; Calling function
Printf(“Enter two numbers a & b”);
Scanf(“%d%d”,&a,&b);
C=add(a,b);
}
Int add(int x,int y)
{
Int z; Called function
Z=x+y;
Return(z);
}
Note: In this example a & b are the actual arguments
x, y are the formal arguments.

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""""
2) Function without return type with arguments.
Void main()
{
void add(int,int);
Int a,b; Calling function
Printf(“Enter two numbers a & b”);
Scanf(“%d%d”,&a,&b);
add(a,b);
}
Int add(int x,int y)
{
Int z; Called function
Z=x+y;
Printf (“%d”,z);
}
Note: In this example a & b are the actual arguments
x, y are the formal arguments.
3) Function with return type without arguments.
Void main()
{
int add( void ); calling function
add(a,b);
}
Int add(void)
{
Int x,y,z;
Printf(“Enter two numbers x & y”);
Scanf(“%d%d”,&x,&y); Called function
Z=x+y;
Return (z);
}
Note: Void means null/no arguments

6. !!!!
""""
4) Function without return type without arguments.
Void main()
{
void add( void ); calling
function
add(a,b);
}
void add(void)
{
Int x,y,z;
Printf(“Enter two numbers x & y”);
Scanf(“%d%d”,&x,&y); Called function
Z=x+y;
Printf (“%d”,z);
}
Note: Void means null/no arguments
Return Statements:
It is jump control statement, when it executes then the control
return to calling function.
Syntax:
Return; it means that it returns statement without values.
Return (value); it means that return a statement with a value.
- Return statement assign value.
- There is more than one return statement present in a function
body with conditions.

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Program: W.A.P input Two no’s and then swap them.
#include<stdio.h>
#include<conio.h>
void main()
{
void swap(int,int);
int a,b;
clrscr();
printf("Enter two no");
scanf("%d%d",&a,&b);
swap(a,b);
//printf("%d%d",a,b);
getch();
}
void swap(int x,int y)
{
int z;
z=x;
x=y;
y=z;
printf("x=%d y=%d",x,y);
}
Program: W.A.P input a no and then reverses it.
#include<stdio.h>
#include<conio.h>
void main()
{
int rev(int);
int no,r;
clrscr();
printf("Enter a no");

8. !!!!
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scanf("%d",&no);
r=rev(no);
printf("%d",r);
getch();
}
int rev(int no1)
{
int r1=0,dg;
while(no1>0)
{
dg=no1%10;
r1=r1*10+dg;
no1=no1/10;
}
return(r1);
}
Program: W.A.P input a no and then check palindrome or not.
#include<stdio.h>
#include<conio.h>
void main()
{
int pali(int);
int no,r;
clrscr();
printf("Enter a no");
scanf("%d",&no);
r=pali(no);
if(r==no)
printf("palindrome");
else
printf("Not palindrome");
getch();

9. !!!!
""""
}
int pali(int no1)
{
int r1=0,dg;
while(no1>0)
{
dg=no1%10;
r1=r1*10+dg;
no1=no1/10;
}
return(r1);
}
Program: W.A.P to find out X ^ Y.
#include<stdio.h>
#include<conio.h>
#include<math.h>
void main()
{
int power(int,int);
int x,y,n;
clrscr();
printf("Enter two no x & y");
scanf("%d%d",&x,&y);
n=power(x,y);
printf("%d",n);
}
int power(int a,int b)
{
int n1=1;
while(b>0)
{
n1=n1*a;

10. !!!!
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b--;
}
return(n1);
}
Program: W.A.P to find out factorial of a no.
#include<stdio.h>
#include<conio.h>
void main()
{
int fact(int);//function prototype
int no,f;
clrscr();
printf("Enter a no");
scanf("%d",&no);
f=fact(no);//actual argument
printf("%d",f);
}
//Function Defination
int fact(int no1)//formal argument
{
int f1=1;
while(no1>0)
{
f1=f1*no1;
no1--;
}
return(f1);
}

11. !!!!
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Program: W.A.P to find out biggest no among three no’s
#include<stdio.h>
#include<conio.h>
void main()
{
int biggest(int,int,int);//function prototype
int a,b,c,d;
clrscr();
printf("Enter three nos");
scanf("%d%d%d",&a,&b,&c);
d=biggest(a,b,c);//actual argument
printf("biggest=%d",d);
}
//Function Defination
int biggest(int x,int y,int z)//formal argument
{
if(x>y&&x>z)
return(x);
else if(y>x&&y>z)
return(y);
else
return(z);
}
Program: C code to print Fibonacci series without recursion:
#include<stdio.h>
void printFibonacci(int);
int main(){
int k,n;
long int i=0,j=1,f;
printf("Enter the range of the Fibonacci series: ");
scanf("%d",&n);

12. !!!!
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printf("Fibonacci Series: ");
printf("%d ",0);
printFibonacci(n);
return 0;
}
void printFibonacci(int n){
long int first=0,second=1,sum;
while(n>0){
sum = first + second;
first = second;
second = sum;
printf("%ld ",sum);
n--;
}
}
Recursion
1. A recursive function is a function which calls itself.
2. The speed of a recursive program is slower because of stack
overheads. (This attribute is evident if you run above C
program.)
3. A recursive function must have recursive conditions,
terminating conditions, and recursive expressions.
Program: Calculating factorial value using recursion
To understand how recursion works lets have another popular
example of recursion. In this example we will calculate the factorial
of n numbers. The factorial of n numbers is expressed as a series of
repetitive multiplication as shown below:
Factorial of n = n (n-1)(n-2)……1.
Example: Factorial of 5 = 5x4x3x2x1=120

13. !!!!
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#include<stdio.h>
#include<conio.h>
int factorial(int);
void main()
{
int x;
clrscr();
printf("Enter any number to calculate factorial :");
scanf("%d",&x);
printf("nFactorial : %d", factorial (x));
getch();
}
int factorial (int i)
{
int f;
if(i==1)
return 1;
else
f = i* factorial (i-1);
return f;
}
Explanation:
Suppose value of i=5, since i is not equal to 1, the statement:
f = i* factorial (i-1);
Will be executed with i=5 i.e.
f = 5* factorial (5-1);
Will be evaluated. As you can see this statement again calls
factorial function with value i-1 which will return value:
4*factorial (4-1);
This recursive calling continues until value of i is equal to 1 and
when i is equal to 1 it returns 1 and execution of this function
stops. We can review the series of recursive call as follow:
f = 5* factorial (5-1);

14. !!!!
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f = 5*4* factorial (4-1);
f = 5*4*3* factorial (3-1);
f = 5*4*3*2* factorial (2-1);
f = 5*4*3*2*1;
f = 120;
Program: C code to find the addition of n numbers by recursion
#include<stdio.h>
int main()
{
int n,sum;
printf("Enter the value of n: ");
scanf("%d",&n);
sum = getSum(n);
printf("Sum of n numbers: %d",sum);
return 0;
}
int getSum(n)
{
int sum=0;
if(n>0){
sum = sum + n;
getSum(n-1);
}
return sum;
}
Sample output:
Enter the value of n: 10
Sum of n numbers: 55

15. !!!!
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Program: Fibonacci series in c by using recursion
#include<stdio.h>
void printFibonacci(int);
int main(){
int k,n;
long int i=0,j=1,f;
printf("Enter the range of the Fibonacci series: ");
scanf("%d",&n);
printf("Fibonacci Series: ");
printf("%d ",0);
printFibonacci(n);
return 0;
}
void printFibonacci(int n){
static long int first=0,second=1,sum;
if(n>0){
sum = first + second;
first = second;
second = sum;
printf("%ld ",sum);
printFibonacci(n-1);
}
}
Sample output:
Enter the range of the Fibonacci series: 10
Fibonacci Series: 0 1 2 3 5 8 13 21 34 55 89

16. !!!!
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Program: Reverse A Number Using Recursion In C Program
#include<stdio.h>
int main(){
int num,rev;
printf("nEnter a number :");
scanf("%d",&num);
rev=reverse(num);
printf("nAfter reverse the no is :%d",rev);
return 0;
}
int sum=0,r;
reverse(int num){
if(num){
r=num%10;
sum=sum*10+r;
reverse(num/10);
}
else
return sum;
return sum;
}