A67641. 运行下面的代码，将出现（ ）。1 double hmean(double a, double b) {

运行下面的代码，将出现（ ）。

1 double hmean(double a, double b) { 
2  if (a == -b ) 
3   throw runtime_error("Runtime error occurred."); 
4  return 2.0*a*b/(a + b); 
5 } 
6
7 int main() { 
8  double x = 10; 
9  double y = -10; 
10
11  try { 
12   int result = hmean(x, y); 
13   cout << "hmean: " << result << endl; 
14  }
15  catch (const runtime_error& e) { 
16   cout << "Caught: " << e.what() << endl; 
17  } catch (...) { 
18   cout << "Caught an unknown exception." << endl; 
19  } 
20  return 0; 
21 }