填写缺失的部分以打印两个数字（由用户输入）的和
int x, y; int sum; cout << "输入一个数字: "; @(3) >> @(1); cout << "输入另一个数字: "; @(3) >> @(1); sum = x + y; cout << "和是: " << @(3);
int x, y; int sum; cout << "输入一个数字: "; cin >> x; cout << "输入另一个数字: "; cin >> y; sum = x + y; cout << "和是: " << sum;