如何在 C++ 中使用字符串数组计算后缀表达式

Question

我试图掌握后缀表达式的概念，我尝试寻求帮助，但我看到的所有地方似乎都在使用常规字符串计算后缀表达式；但是我需要能够用数组来做到这一点

#include <string>
#include <stack>
#include <math.h>

using namespace std;

int calculatePostfixExpression(string expression[], int length)
{
    stack <int> stack;
    // loop to iterate through the expression
    for (int i = 0; i < length; i++)
    {
        // if the character is an operand we push it in the stack
        // we have considered single digits only here
        if ( expression[i] >= "0" &&  expression[i] <= "9")

/*compiler error: no operator "-" matches these operands*/
            { stack.push( expression[i] - "0"); }
        else
        {
            // pop the top two elements from the stack
            int int1 = stack.top();
            stack.pop();
            int int2 = stack.top();
            stack.pop();

/*compiler error: expression must have integral or enum type*/
            switch (expression[i])  
            {

/*compiler error for all cases: this constant has type "const char*" instead of the required "std::string" type*/
                case "+": // addition
                          stack.push(int2 + int1);
                          break;
                case "-": // subtraction
                          stack.push(int2 - int1);
                          break;
                case "*": // multiplication
                          stack.push(int2 * int1);
                          break;
                case "/": // division
                          stack.push(int2 / int1);
                          break;
                case "%": // exponent
                          stack.push(int2 % int1);
                          break;
            }
        }
    }

    return stack.top();
}

我找不到任何地方似乎使用堆栈和字符串数组来做后缀表达式，但提示告诉我使用数组