projecteuler.net : 25. 1000-digit Fibonacci number

25.cpp

/*
 * projecteuler.net
 * 25. 1000-digit Fibonacci number
 * 
 * compile 
 * g++ 25.cpp -o 25 -lgmp -lgmpxx
 */
#include <cstdlib>
#include <iostream>
#include <gmp.h>
#include <gmpxx.h>


int main() {

  mpz_t sum, last_num, current_num;
  mpz_inits(sum, last_num, current_num, NULL);

  mpz_set_str(last_num, "1", 10);
  mpz_set_str(current_num, "1", 10);

  unsigned long long int count = 2;
  unsigned long long int i = 3;

  while (1) {
    //std::cout << last_num << " + " << current_num;
    mpz_add(sum, last_num, current_num);
    mpz_init_set(last_num, current_num);
    mpz_init_set(current_num, sum);
    
    //std::cout << " = " << sum << "\n";
    i++;
    size_t sz = mpz_sizeinbase (sum, 10);
    if (sz == 1000) {
      break;
    }
  }
  
  size_t sz = mpz_sizeinbase (sum, 10);
  std::cout << sum << " | " << sz << " | "<< i << "\n";
}