中缀表达式转换成后缀表达式(只适用于加减乘除运算)

 

 

#include <iostream>
#include <stack>
#include <cctype>

using namespace std;

//获取符号的优先级
int getPriority(char c)
{
    int priority = -1;
    switch (c) {
    case '+':
        priority = 1;
        break;
    case '-':
        priority = 1;
        break;
    case '*':
        priority = 2;
        break;
    case '/':
        priority = 2;
        break;
    case '(':
        priority = 3;
        break;
    default:
        break;
    }
    return priority;
}


int main()
{
    char c;
    stack<char> s;
    cin >> c;
    while (c != '#')
    {
        while (isdigit(c))
        {
            cout << c;
            cin >> c;
            if(!isdigit(c) && c != '#')
                cout << ' ';

        }
        if (c == ')')
        {
            //1.弹出元素并输出直到'('
            while (s.top() != '(')
            {
                cout << s.top() << ' ';
                s.pop();
            }
            //2.将"("也出栈
            s.pop();
        }
        else
        {
            // 下面是普通操作符的情况
            // 1.弹出栈元素直到发现优先级更低的元素
            while (!s.empty() && getPriority(c) <= getPriority(s.top()) && s.top() != '(')
            {
                cout << s.top() << ' ';
                s.pop();
            }
            //将本操作符入栈
            s.push(c);
        }
        cin >> c;
    }
    while (!s.empty())
    {
        cout << s.top() << ' '  ;
        s.pop();
    }
    cout << endl;
    return 0;
}