Using Dijkstra's two-stack algorithm to parse simple arithmetic expressions

two-stack.cpp

#include <iostream>
#include <string>
#include <stack>

void calculate(std::stack<int>& numbers, std::stack<char>& operators);

int main()
{
    std::stack<int> numbers;
    std::stack<char> operators;
    
    for (char c; std::cin >> c; )
    {
        if (std::string("+-*/").find(c) != std::string::npos)
            operators.push(c);
        
        if (std::isdigit(c))
            numbers.push(c - '0');
        
        if (c == ')')
            calculate(numbers, operators);
    }
    
    int result = numbers.top();
    std::cout << result;
}

template <class T>
T pop(std::stack<T>& s)
{
    T popped = s.top();
    s.pop();
    return popped;
}

void calculate(std::stack<int>& numbers, std::stack<char>& operators)
{
    int a = pop(numbers);
    int b = pop(numbers);
    
    char op = pop(operators);
    
    switch (op)
    {
    case '+':
        numbers.push(a + b);
        break;
    case '-':
        numbers.push(a - b);
        break;
    case '/':
        numbers.push(a / b);
        break;
    case '*':
        numbers.push(a * b);
        break;
    }
}