fib.c

#include <stdio.h>

int fib(int x)
{
    long int ret = 1;
    int l1 = 0, l2 = 0;
    int i;

    for (i = 0; i < x; i++)
    {
        ret += l1;
        l1  = l2;
        l2  = ret;
    }

    return ret;
}

int main(void)
{
    int i;

    for (i = 0; i <= 50; i++)
    {
        printf("%-2d: %ld\n", i, fib(i));
    }

    return 0;
}