C Program for Fibonacci Series

Summary: in this tutorial, you will learn how to develop a C program for Fibonacci series using recursion and iteration techniques.

Introduction to Fibonacci numbers

In mathematics, the Fibonacci numbers, or Fibonacci series,  are the numbers that are in the following sequence:

0,1,1,2,3,5,6,13,21,34,55,89,…

The first number in the Fibonacci sequence is 0, the second number is 1. The subsequent number is the result of the sum of the previous two e.g., third number 1 = 1+0, fourth number 2=1+1, fifth number 3 = 2+1, etc.

The Fn number is defined as follows:

Fn = Fn-1 + Fn-2,

with the seed values:

F0 = 0, F1 = 1.

C Programs for Fibonacci Series

C Program for Fibonacci series using recursion

The first simple approach of developing a function that calculate the nth number in the Fibonacci series using a recursive function. The following is Fibonacci series program in c:

#include <stdio.h>

typedef unsigned long long F;

F fibonacci(F n);

int main()
{
    int n, i, j;

    printf("--- Fibonacci series program ---\n");
    printf("Enter a number:");
    scanf("%d",&n);

    printf("\nFibonacci series:\n");
    j = 0;
    for ( i = 1 ; i <= n ; i++ )
    {
        printf("%d ", fibonacci(j));
        j++;
    }
}

F fibonacci(F n)
{
    if ( n == 0 )
        return 0;
    if ( n == 1 )
        return 1;

    return fibonacci(n-1) + fibonacci(n-2);
}

Now if you enter 15, the program will display the following output:

--- Fibonacci series program ---
Enter a number:15

Fibonacci series:
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

C Program for Fibonacci series using iteration

The Fibonacci series program using recursion technique is less efficient if you want to display a long series because the number of function calls increase and the chance of a stack overflow error may occur.

The following is the program that displays the Fibonacci series using iteration technique:

#include <stdio.h>

typedef unsigned long long F;

F fibonacci(F n);

int main()
{
    int n, i, j;

    printf("--- Fibonacci series program ---\n");
    printf("Enter a number:");
    scanf("%d",&n);

    printf("\nFibonacci series:\n");
    j = 0;
    for ( i = 1 ; i <= n ; i++ )
    {
        printf("%d ", fibonacci(j));
        j++;
    }
}

F fibonacci(F n)
{
    int i;
    F f1 = 0;
    F f2 = 1;
    F fi;

    if(n == 0)
        return 0;
    if(n == 1)
        return 1;

    for(i = 2 ; i <= n ; i++ )
    {
        fi = f1 + f2;
        f1 = f2;
        f2 = fi;
    }
    return fi;
}

In this tutorial, you have learned how to develop a C program for Fibonacci series using recursion and iteration techniques.