如何从输入中提取？

Question

How do you calculate, given that the input is as follows?

All the questions are in the format of You also took note that all the numbers were positive integers and there were only 3 types of operators: +, - and *.

Sample Input 1

5 - 3

Sample Output 1

2

Sample Input 2

7 * 7

Sample Output 2

49

Sample Input 3

13 + 4

Sample Output 3

17

Answer 1

You are tasked to write a calculator in https://en.wikipedia.org/wiki/Reverse_Polish_notation . There are many tutorials on the web on how to do this.

Answer 2

Well, since you have no requirements in regards to implementation, a simple switch statement would do. Here's a simple example implementation. If you are new to C++, note down std::cerr .

#include <iostream>
#include <cstdlib>

int main()
{
  int a, b;
  char op;
  std::cin >> a >> op >> b;
  switch (op)
  {
    case '+':
    {
      std::cout << a + b << std::endl;
      break;
    }
    case '-':
    {
      std::cout << a - b << std::endl;
      break;
    }
    case '*':
    {
      std::cout << a * b << std::endl;
      break;
    }
    default:
    {
      std::cerr << "Invalid operator" << std::endl;
      return EXIT_FAILURE;
    }
  }
  return EXIT_SUCCESS;
}