python/TangDou/FourArithmeticOperation/FourArithmeticOperation.cpp

// https://blog.csdn.net/amf12345/article/details/96868717

#include<bits/stdc++.h>

using namespace std;

//四则运算的类
class fourArithmeticOperation {

public:
    //四则运算的字符串
    string s;
    //数字栈
    stack<int> val;
    //操作符栈
    stack<char> symbol;

    //构建函数
    fourArithmeticOperation() {
        symbol.push('#');
    }

    //表达式计算的过程
    int process() {
        int i = 0, num;
        while (symbol.top() != '#' || i < s.size()) {
            //发现了数字
            if (s[i] >= '0' && s[i] <= '9') {
                //为操作数
                num = 0;
                //根据字符串转为数字的方法
                while (s[i] >= '0' && s[i] <= '9') {//一直向后找是数字的
                    num *= 10;
                    num += s[i] - '0';
                    ++i;
                }
                //数字入栈
                val.push(num);
                cout << num << "入栈val" << endl;
            } else {
                switch (cmp(symbol.top(), s[i])) {
                    case '<':
                        symbol.push(s[i]);
                        //调试信息
                        cout << s[i] << "入栈symbol" << endl;
                        ++i;
                        break;
                    case '=': //用于前后等号对掉
                        //调试信息
                        cout << symbol.top() << "出栈symbol" << endl;
                        symbol.pop();
                        ++i;
                        break;
                    case '>':
                        int a = val.top();
                        val.pop();
                        int b = val.top();
                        //出栈
                        cout << b << "出栈val" << endl;
                        val.pop();
                        val.push(cal(b, a, symbol.top()));
                        //调试信息
                        cout << a << symbol.top() << b << "=" << val.top() << endl;
                        cout << val.top() << "入栈val" << endl;
                        //出栈
                        cout << symbol.top() << "出栈symbol" << endl;
                        symbol.pop();
                        break;
                }
            }
        }
        int res = val.top();
        val.pop();
        return res;
    }


    //操作符之间的优先级的比较
    char cmp(char a, char b) {
    //右括号不会进栈，不必写右括号的优先级
    //遇到右括号就弹出左括号
        if (a == '#') {
            if (b == '#') {
                return '=';
            } else {
                return '<';
            }
        }
        if (a == '+' || a == '-') {
            if (b == '*' || b == '/' || b == '(') {
                return '<';
            } else {
                return '>';
            }
        }
        if (a == '*' || a == '/') {
            if (b == '(') {
                return '<';
            } else {
                return '>';
            }
        }
        if (a == '(') {
            if (b == ')') {
                return '=';
            } else {
                return '<';
            }
        }
    }

//返回计算结果
    int cal(int a, int b, char op) {
        switch (op) {
            case '+':
                return a + b;
            case '-':
                return a - b;
            case '*':
                return a * b;
            case '/':
                return a / b;
        }
    }

};

int main() {
    fourArithmeticOperation s1;
    //测试用例:  (1+2)*(4-3)
    s1.s = "(1+2)*(4-3)";
    cout << s1.process() << endl;

    //换行
    cout << endl;

    //测试用例:  (4-2)/2*3-4;
    s1.s = "(4-2)/2*3-4";
    cout << s1.process() << endl;
    return 0;
}