Infix to Postfix

Oct 10, 2022 · 1 min read

Question

Convert infix expression to postfix expression using C++

Some Important Concepts

Infix notation is the notation in which operators come between the required operands.
Postfix notation is the type of notation in which operator comes after the operand.
Infix expression can be converted to postfix expression using stack.

Code

#include<iostream>
#include<math.h>
#include<stack>
using namespace std;
int precedence(char c){
    if (c=='^')
    {
        return 3;
    }
    else if (c=='*'||c=='/')
    {
        return 2;
    }
    else if(c=='+'||c=='-'){
        return 1;
    }
    else{
        return -1;
    }
}
string infixToPostfix(string s){
    stack<char> st;
    string result;
    for(int i = 0; i < s.length(); i++){
        if(s[i]>='a'&&s[i]<='z'||s[i]>='A'&&s[i]<='Z'){
            result+=s[i];    
        }
        else if(s[i]=='('){
            st.push(s[i]);
        }
        else if(s[i]==')'){
            while(!st.empty()&&st.top()!='('){
                result+=st.top();
                st.pop();
            }
            if (!st.empty())
            {
                st.pop();
            } 
        }
        else{
            while (!st.empty()&&precedence(st.top())>precedence(s[i]))
            {
                result+=st.top();
                st.pop();
            } 
            st.push(s[i]);
        }
    }
    while (!st.empty())
    {
        result+=st.top();
        st.pop();
    }
    
    return result;
}
int main(){

   cout<<infixToPostfix("(a-b/c)*(a/k-l)")<<endl;

return 0;
}

Output

abc/-ak/l-*