Fibonacci Number (http://cs.iit.edu/~khale/class/vm-class/f19/handout/p1.html)

fib.c

// Nth fibonacci number
#define N 10

#include <stdio.h>

long fib(int n) {
    long prevFib = 0;
    long fib = 1;
    int i;
    for(i=2; i<=n; i++) {
        long nextFib = fib + prevFib;
        prevFib = fib;
        fib = nextFib;
    }
    return fib;
}

int main() {
    printf("%ld\n", fib(N));
    return 0;
}