Recursion in C Programming

In C programming language, a function that calls itself is known as a recursive function. And, this technique is called as recursion.

 Recursive functions are very useful to solve many problems such as  Towers of Hanoi (TOH), Inorder/Preorder/Postorder Tree Traversals, DFS of Graph, etc.

How recursion works?

 void recurse()
	{
 	   ... .. ...
  	  recurse();
  	  ... .. ...
	}

	int main()
	{
   	 ... .. ...
   	 recurse();
   	 ... .. ...
	}	

Example: Write a program in a C language to find the factorial using recursion.

#include 
long int factorial(int n);

int main()
{
    int n;
    printf("Enter a number to find factorial: ");
    scanf("%d", &n);
    printf("Factorial of %d = %ld", n, factorial(n));
    return 0;
}
long int factorial(int n)
{
    if (n >= 1)
        return n*factorial(n-1);
    else
        return 1;
}

OUTPUT

Enter a number to find factorial: Factorial of 5 = 120

Example: Write a program in a C language to print the Fibonacci series using recursion.

Fibonacci series are 0, 1, 1, 2, 3, 5, 8, …,. 

In fibonacci series, except for the first two terms of the series, every other term is the sum of the previous two terms, for example, 5 = 2 + 3.

#include
 int fibonacci(int);
 
int main()
{
  int n, i = 0, c;
  printf("Enter the nth number in fibonacci series "); 
  scanf("%d", &n);
 
  	printf("\n Fibonacci series terms are:\n");
 
  	for (c = 1; c <= n; c++)
  	{
    		printf("%d\n", fibonacci(i));
    		i++;
  	}
 
  return 0;
}
 
int fibonacci(int n)
{
  	if (n == 0 || n == 1)
    		return n;
  else
   		 return (fibonacci(n-1) +fibonacci(n-2));
}

Enter the nth number in fibonacci series 
10
Fibonacci series terms are:
0
1
1
2
3
5
8
13
21
34