infixToPostfixUsingSTLStack.cpp

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

int isOperand(char x)
{
    if (x == '+' || x == '-' || x == '*' || x == '/' || x == '^' || x == '(' || x == ')')
        return 0;
    return 1;
}

int outPrecedence(char x)
{
    if (x == '+' || x == '-')
        return 1;
    else if (x == '*' || x == '/')
        return 3;
    else if (x == '^')
        return 6;
    else if (x == '(')
        return 7;
    else if (x == ')')
        return 0;
    return -1;
}

int inPrecendence(char x)
{
    if (x == '+' || x == '-')
        return 2;
    else if (x == '*' || x == '/')
        return 4;
    else if (x == '^')
        return 5;
    else if (x == ')')
        return 0;
    return -1;
}

char *Convert(char *infix)
{
    char *postfix = new char[strlen(infix) + 1];
    stack<char> stk;
    int i = 0, j = 0;
    while (infix[i] != '\0')
    {
        if (isOperand(infix[i]))
        {
            postfix[j++] = infix[i++];
        }
        else
        {
            if (stk.empty() || outPrecedence(infix[i]) > inPrecendence(stk.top()))
            {
                stk.push(infix[i++]);
            }
            else if (outPrecedence(infix[i]) > inPrecendence(stk.top()))
            {
                stk.pop();
            }
            else
            {
                postfix[j++] = stk.top();
                stk.pop();
            }
        }
    }

    while (!stk.empty() && stk.top() != ')')
    {
        postfix[j++] = stk.top();
        stk.pop();
        return postfix;
    }
}

int main()
{
    char infix[] = "((a+b)*c)-d^e^f";
    cout << Convert(infix) << endl;
    return 0;
}