iterfibonacci.c

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

uint64_t iterfibonacci(uint64_t n)
{
	uint64_t x=1, y=1, z=1, counter;

	for (counter = 2; counter < n; ++counter) {
		z = x + y;
		x = y;
		y = z;
	}

	return z;
}

int main(int argc, char** argv)
{
	uint64_t n = strtoull(argv[1], NULL, 0);

	printf("Fibonacci(%" PRIu64 ") = %" PRIu64 "\n", n, iterfibonacci(n));

	return EXIT_SUCCESS;
}