C Programming

• Recursion is a process by which a function calls itself repeatedly, until some specified condition has been satisfied.
• The process is used for repetitive computations in which each action is stated in terms of a previous result.
• In order to solve a problem recursively, two conditions must be satisfied.
• First, the problem must be written in a recursive form, and second, the problem statement must include a stopping condition

Example:

Suppose, for example, we wish to calculate the factorial of a positive integer quantity.

We would normally express this problem as:

 n! = 1 × 2 × 3 × . . . . × n

where n is the specified positive integer

However, we can also express this problem in another way by writing:

n! = n × ( n – 1 ) !

• This is a recursive statement of the problem, in which the desired action ( the calculation of n!) is expressed in terms of a previous result [ the value of ( n-1 )!, which is assumed to be known].
• Also, we know that 1! = 1, by definition.
• This last expression provides a stopping condition for the recursion.

Calculating Factorial Using Recursion

# include <stdio.h>

long int factorial ( int n) {
	
	if ( n <= 1)
	
	return 1;
	
	else
	
	return ( n * factorial ( n – 1 ));
	
}

void main ( void ) 

{
	
	printf ( “\n 5! = %ld”, factorial(5)); 
	
}