fib.c

/*
Calculate the nth Fibonacci number. 
example usage: ./fib 50 
(Calculates the 50th fibonacci number) 

(Do what you want with this)
https://opensource.org/license/0bsd/
Zero-Clause BSD
===============

Permission to use, copy, modify, and/or distribute this software for
any purpose with or without fee is hereby granted.

THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL
WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE
FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY
DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

// Calculate Fibonacci Numbers 
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <ctype.h>
#include <gmp.h>

long limit, i = 0; 

int main(int argc, char *argv[])
{
	// Get User Input 
	if (argc != 2)
	{
		printf("Improper input. Exiting.\n");
		return -1; 
	}

	limit = strtol(argv[1], NULL, 10);

	// Setup GMP 
	mpz_t a, b, c;
	mpz_init_set_ui(a, 1);
    	mpz_init_set_ui(b, 0);
   	mpz_init(c);

   	for (i = 0; i < limit; i++)
   	{
   		// Perform the Fibonacci Calculation
   		mpz_add(c, a, b);
   		mpz_set(a, b);
   		mpz_set(b, c);
   	}

	// Print the results to stdout
   	printf("Fibonacci Number %ld: ", i);
   	mpz_out_str(stdout, 10, b);
   	printf("\n");

	// Cleanup
   	mpz_clear(a);
   	mpz_clear(b);
   	mpz_clear(c);
	
	
	return 0;
}