C Recursions

Recursion is the repeated application of a recursive procedure or definition. A recursive function can simulate a loop by call itself multiple times until a base condition is satisfied. A recursive function without an exit or base condition will fall into an infinite loop.

Syntax

void recursive_func()
{
    //body
    recursive_func();
}

Recursive function using main()

The main() function can be made into a recursive function by calling it from within the body.

void main()
{
    //body
    main();
}

Fibonacci Series using Recursion

Fibonacci series F_n is defined as a series of numbers in which each number ( Fibonacci number ) is the sum of the two preceding numbers.

F₀ = 0, F₁ = 1, and
F_n = F_n-1 + F_n-2 , for n > 1.

therefore, Fibonacci Series := 0, 1, 1, 2, 3, 5, 8, 13, ...

Code

#include <stdio.h>

int fibonacci(int);

int main(void) 
{
    int no_of_terms,i;
    printf("Enter the number of terms: ");
    scanf("%d", &no_of_terms);
    
    printf("Fibonacci Series: ");
    
    for ( i = 0 ; i < no_of_terms ; i++ )
   {
        //function call
        printf("%d ", fibonacci(i));
   }

    return 0;
}

int fibonacci(int n)
{  
    //base condition
    if ( n == 0 || n == 1)
        return n;
    
    //recursive call
    else
        return ( fibonacci(n-1) + fibonacci(n-2) );
}

Output

Enter the number of terms: 10
Fibonacci Series: 0 1 1 2 3 5 8 13 21 34