C Programming Code Examples

C > For Loops and While Loops Code Examples

Program to print Fibonacci series in given range

Program to print Fibonacci series in given range

What is Fibonacci series?

Fibonacci series is a series of numbers where the current number is the sum of previous two terms. For Example: 0, 1, 1, 2, 3, 5, 8, 13, 21, ... , (n-1th + n-2th)
Logic to print Fibonacci series upto n terms

    Input number of Fibonacci terms to print from user. Store it in a variable say terms.
    Declare and initialize three variables, I call it as Fibonacci magic initialization. a=0, b=1 and c=0.

    Here c is the current term, b is the n-1th term and a is n-2th term.
    Run a loop from 1 to terms, increment loop counter by 1. The loop structure should look like for(i=1; i<=term; i++). It will iterate through n terms
    Inside the loop copy the value of n-1th term to n-2th term i.e. a = b.

    Next, copy the value of nth to n-1th term b = c.

    Finally compute the new term by adding previous two terms i.e. c = a + b.
    Print the value of current Fibonacci term i.e. c.

#include <stdio.h>

int main()
{
    int a, b, c, start, end;

    /* Input a number from user */
    printf("Enter starting term: ");
    scanf("%d", &start);
    printf("Enter end term: ");
    scanf("%d", &end);

    /* Fibonacci magic initialization */
    a = 0;
    b = 1;
    c = 0;

    printf("Fibonacci terms: \n");

    /* Iterate through terms */
    while(c <= end)
    {

        /* If current term is greater than start term */
        if(c >= start) 
        {
            printf("%d, ", c);
        }

        a = b;     // Copy n-1 to n-2
        b = c;     // Copy current to n-1
        c = a + b; // New term
    }

    return 0;
}