fibonacci c++ gmp generator

你好，我正在尝试将gmp实现到我编写的现有fibonacci生成器中。我一直在仔细阅读gmp文档，但仍然有很多我不理解的地方。最初的斐波那契生成器在这里：

#include <iostream>
using namespace std;
class Fib {
  int n; 
  long unsigned int first, second;
public:
  Fib() {
    first = 0;
    second = 1;
    cout << "Enter the number of terms of Fibonacci series you want" << endl;
    cin >> n;
    cout << "First " << n << " terms of Fibonacci series are:" << endl;
  }
  int solve() {
    int i; 
    long unsigned int next;
    for(i = 0 ; i < n + 1 ; i++) {
      if(i <= 1) {
        next = i;
      }
      else {
        next = first + second;
        first = second;
        second = next;
      }
    }
    return next;
  }
};
int main() {
  Fib fib;
  cout << fib.solve() << endl;
  return 0; 
}

我安装gmp使用：

sudo apt-get-install libgmp3-dev

当我尝试实现gmp时，我这样做了：

#include <iostream>
#include <gmpxx.h>
using namespace std;
class Fib {
  int n; 
  mpz_class first, second;
public:
  Fib() {
    first = 0;
    second = 1;
    cout << "Enter the number of terms of Fibonacci series you want" << endl;
    cin >> n;
    cout << "First " << n << " terms of Fibonacci series are:" << endl;
  }
  int solve() {
    int i; 
    mpz_class next;
    for(i = 0 ; i < n + 1 ; i++) {
      if(i <= 1) {
        next = i;
      }
      else {
        next = first + second;
        first = second;
        second = next;
      }
    }
    return next;
  }
};
int main() {
  Fib fib;
  cout << fib.solve() << endl;
  return 0; 
}

我知道在某个时候我需要将int转换为字符串，然后清除输出变量或类似的东西。当我尝试编译时，我运行：

g++-lgmpxx-lgmp-fib.cpp-o fib

我的输出：

fib.cpp: In member function ‘int Fib::solve()’:
fib.cpp:30:12: error: cannot convert ‘mpz_class {aka __gmp_expr<__mpz_struct [1],     __mpz_struct [1]>}’ to ‘int’ in return
     return next;
            ^

我是bignum库的一个完全的noob，任何帮助都将是伟大的。我正在阅读文档，但我正在努力实现它。