C++ 计算器运算符

Question

我的代码有问题，每次我输入除运算符 (+,/,*,-) 以外的其他内容时，它仍然会要求输入数字。我希望它停止并显示文本“错误！运算符不正确”，当有人将其他东西放在运算符之外时

#include <iostream>
using namespace std;
int main()
{
    char op;
    float num1, num2;
    cout << "Enter operator either + or - or * or /: ";
    cin >> op;
    cout << "Enter the first operand: ";
    cin >> num1;
    cout << "Enter the second operand: ";
    cin >> num2;

    switch (op)
    {

    case '+':
        cout << num1 + num2;
        break;
    case '-':
        cout << num1 - num2;
        break;
    case '*':
        cout << num1 * num2;
        break;
    case '/':
        cout << num1 / num2;
        break;

    default:
        cout << "Error! operator is not correct";
        break;
    }
    return 0;
}

提前致谢 enter image description here

Answer 1

听起来您想要清除输入？

如果您希望某些输入被拒绝，那么在输入之后，您需要清除标准输入。

cin.clear();
cin.ignore(1000, '\n');

完成此操作后不要忘记再次请求输入，否则不会发生任何事情。 考虑把它放在一个while循环中并循环：

• 询问接线员
• 如果是接线员，请询问号码
• 否则清除输入并再次请求操作员

希望这会有所帮助！

Answer 2

你把cin输入操作放错地方了。如果您希望您的代码在输入错误的运算符后立即输出错误，则必须在检查运算符后移动cin部分，或者遇到无法识别的运算符时提前退出程序。

#include <iostream>
using namespace std;

void askNum(float &num1, float &num2)  //passing the values by reference 
{
    cout << "Enter the first operand: ";
    cin >> num1;
    cout << "Enter the second operand: ";
    cin >> num2;
}

int main()
{
    char op;
    float num1, num2;
    cout << "Enter operator either + or - or * or /: ";
    cin >> op;

    switch (op)
    {
        case '+':
            askNum(num1, num2);
            cout << num1 + num2;
            break;
        case '-':
            askNum(num1, num2);
            cout << num1 - num2;
            break;
        case '*':
            askNum(num1, num2);
            cout << num1 * num2;
            break;
        case '/':
            askNum(num1, num2);
            cout << num1 / num2;
            break;

        default:
            cout << "Error! operator is not correct";
            break;
    }

    return 0;
}

或使用您的代码，但像这样添加return 0：（它有效，但我不推荐这样做）

default:
    cout << "Error! operator is not correct";
    return 0;

Answer 3

也许你想试试这个？

#include <stdio.h>
#include <iostream>
#include <unordered_map>
#include <functional>
using namespace std;

unordered_map < char,function < float (float, float) >>
  op_mapper{
  {'+', std::plus < float >()},
  {'-', std::minus < float >()},
  {'*', std::multiplies < float >()},
  {'/', std::divides < float >()}};
int main ()
{
  char op;
  float num1,num2;
  while (op != 'q') {
      cout << "Enter operator either + or - or * or /: ";
      cin >> op;

      if (op_mapper.find (op) != op_mapper.end ()) {
      cout << "Enter the first operand: ";
      cin >> num1;
      cout << "Enter the second operand: ";
      cin >> num2;
      cout << op_mapper[op] (num1, num2) << endl;
    } else {
      cout << "Error! operator is not correct";
    }
  }

  return 0;
}

Answer 4

读完运算符后，你需要检查运算符是否正确。下面的代码解决了你的问题。

代码

#include <iostream>
using namespace std;
int main()
{
    char op;
    float num1, num2;
    cout << "Enter operator either + or - or * or /: ";
    cin >> op;

    if(op == '+' || op == '-'|| op == '*'|| op == '/'){
        cout << "Enter the first operand: ";
        cin >> num1;
        cout << "Enter the second operand: ";
        cin >> num2;    

    }else{
        cout << "Error! operator is not correct";
        return 0 ;
    }

    switch (op)
    {
        case '+':
            cout << num1 + num2;
            break;
        case '-':
            cout << num1 - num2;
            break;
        case '*':
            cout << num1 * num2;
            break;
        case '/':
            cout << num1 / num2;
            break;
    }    

    return 0;
}