fib.c

#include <stdio.h>

int fib(int n) {
    if (n == 1 || n == 2) {
        return 1;
    } else {
        return fib(n-1) + fib(n-2);
    }
}

int main() {
    printf("%d\n", fib(45));
    return 0;
}

/* > gcc -O0 -o fib-c fib.c; /usr/bin/time ./fib-c
 * 1134903170
 * 5.78user 0.00system 0:05.79elapsed 99%CPU (0avgtext+0avgdata 1376maxresident)k
 * 0inputs+0outputs (0major+64minor)pagefaults 0swaps
 */

/* > gcc -O2 -o fib-c fib.c; /usr/bin/time ./fib-c
 * 1134903170
 * 2.39user 0.00system 0:02.39elapsed 99%CPU (0avgtext+0avgdata 1380maxresident)k
 * 0inputs+0outputs (0major+65minor)pagefaults 0swaps
 */