数据结构 算术表达式求值 C++ 栈方法

#include <iostream>
#include <stack>
#include <string>
using namespace std;

int evaluateExpression(string expression) {
    stack<int> operandStack;
    stack<char> operatorStack;

    istringstream tokens(expression);
    string token;
    const string operators = "+-*/";

    while (tokens >> token) {
        if (token[0] == '+' || token[0] == '-') {
            while (!operatorStack.empty() && (operatorStack.top() == '+' || operatorStack.top() == '-' ||
                   operatorStack.top() == '*' || operatorStack.top() == '/')) {
                processAnOperator(operandStack, operatorStack);
            }
            operatorStack.push(token[0]);
        } else if (token[0] == '*' || token[0] == '/') {
            while (!operatorStack.empty() && (operatorStack.top() == '*' || operatorStack.top() == '/')) {
                processAnOperator(operandStack, operatorStack);
            }
            operatorStack.push(token[0]);
        } else if (token[0] == '(') {
            operatorStack.push('(');
        } else if (token[0] == ')') {
            while (operatorStack.top() != '(') {
                processAnOperator(operandStack, operatorStack);
            }
            operatorStack.pop();
        } else {
            operandStack.push(stoi(token));
        }
    }

    while (!operatorStack.empty()) {
        processAnOperator(operandStack, operatorStack);
    }

    return operandStack.top();
}

void processAnOperator(stack<int>& operandStack, stack<char>& operatorStack) {
    char op = operatorStack.top();
    operatorStack.pop();
    int op1 = operandStack.top();
    operandStack.pop();
    int op2 = operandStack.top();
    operandStack.pop();
    if (op == '+') {
        operandStack.push(op2 + op1);
    } else if (op == '-') {
        operandStack.push(op2 - op1);
    } else if (op == '*') {
        operandStack.push(op2 * op1);
    } else if (op == '/') {
        operandStack.push(op2 / op1);
    }
}

int main() {
    string expression = "3 + 4 * 5";
    cout << "The result of the expression is: " << evaluateExpression(expression) << endl;
    return 0;}