infix2postfix

最新推荐文章于 2020-04-13 01:07:06 发布

原创最新推荐文章于 2020-04-13 01:07:06 发布 · 404 阅读

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CC 4.0 BY-SA版权

本文介绍了一种使用栈数据结构将中缀表达式转换为后缀表达式（逆波兰表示法）的方法。通过分析输入的数学表达式，该程序能够正确处理括号、乘除加减运算符以及指数运算。

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

int main()
{
    stack<char> s; // use a stack to store the character of the equation
    string equation; // store the whole equation
    getline (cin, equation);
    int cur = 0; // the current position in the equation

    while (cur < equation.size())
    {
        while (equation[cur] == ' ')
            cur++;

        if (equation[cur] >= 'a' && equation[cur] <= 'z')
            cout<< equation[cur] << " ";

        else if (equation[cur] == ')')
        {
            while(!s.empty() && s.top() != '(') // if equation[cur] equals ')', then pop out all the character until '('
            {
                cout<< s.top() << " ";
                s.pop();
            }
            s.pop(); // pop out the '('
        }   

        else if (equation[cur] == '(') // '(' has the highest priority, put it into the stack directly
            s.push(equation[cur]); 

        else if (equation[cur] == '^')  // '^' has the highest priority except for the parenthesis
            s.push(equation[cur]); 

        else if (equation[cur] == '*' || equation[cur] == '/') //
        {
            while(!s.empty() && s.top() != '+'&& s.top() != '-' && s.top() != '(') //'*' and '/' have the same priority
            {
                cout<< s.top() << " "; 
                s.pop();
            }
            s.push(equation[cur]);
        }

        else if (equation[cur] == '+' || equation[cur] == '-') //'+' and '-' have the same priority
        {
            while(!s.empty() && s.top() != '(' )
            {
                cout<< s.top() << " ";
                s.pop();
            }
            s.push(equation[cur]); 
        } 

    cur++; // to process the next character
    }

    while (!s.empty())
    {
        cout << s.top() << " ";
        s.pop();
    }
    return 0;
}