infixtopostfix.cpp

#include<bits/stdc++.h>
using namespace std;

int prec(char c) {
    if(c == '^')
        return 3;
    else if(c == '/' || c=='*')
        return 2;
    else if(c == '+' || c == '-')
        return 1;
    else
        return -1;
}

void infixToPostfix(string s) {

    stack<char> st;
    string result;

    for(int i = 0; i < s.length(); i++) {
        char c = s[i];

        if((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9'))
            result += c;

        else if(c == '(')
            st.push('(');

        else if(c == ')') {
            while(st.top() != '(')
            {
                result += st.top();
                st.pop();
            }
            st.pop();
        }

        else {
            while(!st.empty() && prec(s[i]) <= prec(st.top())) {
                result += st.top();
                st.pop();
            }
            st.push(c);
        }
    }

    while(!st.empty()) {
        result += st.top();
        st.pop();
    }

    cout<<"Postfix Expression: "<<result<<endl;
}

int main() {
    string exp;
    cout<<"Enter Infix Expression: ";
    cin>>exp;
    infixToPostfix(exp);
    return 0;
}