fib_test.c

#include <stdlib.h>
#include <stdio.h>

extern unsigned long fib(unsigned long);

int main(int argc, char* argv[]) {
  if(argc<2) printf("usage: fib_test <integer>\n"), exit(1);
  unsigned long input = strtoul(argv[1],NULL,10); // string to unsigned long
  printf("fib(%lu) = %lu\n",input,fib(input));
  return 0;
}