运行下面的代码，屏幕上将输出（    ）。

#include <iostream>

using namespace std;

int divide(int a, int b) {

      if (b == 0) {

            throw runtime_error("division by zero error ");

      }

      return a / b;

}

int main() {

      int x = 10;

      int y = 0; // 设为 0 会导致除零错误

      try {

            int result = divide(x, y);

            cout << "result: " << result << endl;

      } catch (const runtime_error& e) {

            cout << "caught an exception: " << e.what() << endl;

      }

      return 0;

}