cin >> num1,num2有什么问题？

Question

#include <iostream>
using namespace std;

int main() {
  char choice;
  int solution, num1, num2;

  cout << "Menu";
  cout << "\n========";
  cout << "\n+) Add";
  cout << "\n-) subtract";
  cout << "\n*) Multiplication";
  cout << "\n/) Division";
  cout << "\nx) Exit";
  cout << endl;
  cout << "\nEnter your choice: ";
  cin >> choice;

  switch (choice) {
    case '+':
      cout << "\nEnter the operands: ";
      cin >> num1, num2;
      solution = num1 + num2;
      cout << num1 << '+' << num2 << '=' << solution;
      break;
    case '-':
      cout << "\nEnter the operands: ";
      cin >> num1, num2;
      solution = num1 + num2;
      cout << num1 << '-' << num2 << '=' << solution;
      break;
    case '*':
      cout << "\nEnter the operands: ";
      cin >> num1, num2;
      solution = num1 * num2;
      cout << num1 << '*' << num2 << '=' << solution;
      break;
    case '/':
      cout << "\nEnter the operands: ";
      cin >> num1, num2;
      solution = num1 / num2;
      cout << num1 << '/' << (double)num2 << '=' << solution;
      break;
    case 'x':
    case 'X':
      cout << "\nExiting....";
      return 0;
      break;
    default:
      cout << "\nInvalid choice";
  }

  return 0;
}

所以我正在编写一个允许用户输入操作的程序.它几乎是一个计算器!我必须使用switch语句.我觉得我很亲密,但现在我已经打了一堵砖墙.在用户启动操作之后,程序运行并说它进入操作数,然后它应该用输入的数字进行操作并显示它们.在用户输入程序崩溃的2个操作数之后,这是一些问题.有什么建议吗？

Answer 1

cin >> num1, num2;

此语法不适合您的需要.链,使用

cin >> num1 >> num2;

如果您使用警告进行编译,编译器将通知您

int a{}, b{};
std::cin >> a, b;

给出错误:

warning: right operand of comma operator has no effect [-Wunused-value]
std::cin >> a, b;

整个语句被解析为

((std::cin >> a), b);

其中包含两个以逗号分隔的表达式.该b在这种情况下,没有任何效果.如果您在打印后的变量std::cin线之上,你总是会得到0的b