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;
}