检查前缀表达式检查语法合法性的代码c++，要求有当输入的不是前缀表达式或除数为0时是要显示“错误

当输入的不是前缀表达式或除数为0时显示错误的代码示例（C++）如下所示：

#include <iostream>
#include <stack>
#include <sstream>

bool isOperator(const std::string& token) {
    return (token == "+" || token == "-" || token == "*" || token == "/");
}

bool isNumber(const std::string& token) {
    std::istringstream iss(token);
    double num;
    iss >> num;
    return !iss.fail();
}

bool isValidPrefixExpression(const std::string& expr) {
    std::istringstream iss(expr);
    std::stack<std::string> stack;
    std::string token;

    while (iss >> token) {
        if (isOperator(token)) {
            if (stack.size() < 2) {
                return false; // Invalid expression: not enough operands
            }
            stack.pop();
        }
        else if (isNumber(token)) {
            stack.push(token);
        }
        else {
            return false; // Invalid expression: invalid token
        }
    }

    return (stack.size() == 1);
}

double evaluatePrefixExpression(const std::string& expr) {
    std::istringstream iss(expr);
    std::stack<double> stack;
    std::string token;

    while (iss >> token) {
        if (isOperator(token)) {
            if (stack.size() < 2) {
                throw std::runtime_error("Invalid expression: not enough operands");
            }
            double operand2 = stack.top();
            stack.pop();
            double operand1 = stack.top();
            stack.pop();
            
            if (token == "+")
                stack.push(operand1 + operand2);
            else if (token == "-")
                stack.push(operand1 - operand2);
            else if (token == "*")
                stack.push(operand1 * operand2);
            else if (token == "/") {
                if (operand2 == 0) {
                    throw std::runtime_error("Error: Division by zero");
                }
                stack.push(operand1 / operand2);
            }
        }
        else if (isNumber(token)) {
            std::istringstream issNum(token);
            double num;
            issNum >> num;
            stack.push(num);
        }
    }

    if (stack.size() == 1) {
        return stack.top();
    }
    else {
        throw std::runtime_error("Invalid expression: too many operands");
    }
}

int main() {
    std::string expr;
    std::cout << "Enter a prefix expression: ";
    std::getline(std::cin, expr);

    if (isValidPrefixExpression(expr)) {
        try {
            double result = evaluatePrefixExpression(expr);
            std::cout << "Result: " << result << std::endl;
        }
        catch (const std::runtime_error& error) {
            std::cout << "Error: " << error.what() << std::endl;
        }
    }
    else {
        std::cout << "Invalid prefix expression" << std::endl;
    }

    return 0;
}

这段代码可以检查输入是否为前缀表达式，并计算其结果。如果输入的不是前缀表达式或除数为0，则会显示相应的错误信息。