Answers for "convert infix to postfix"

infix to postfix conversion

Best Solution
-------------------------------------------------------------------
#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;
    }
}

string infixToPostfix(string s) {
    stack<char> st;
    string res;

    for (int i = 0; i < s.length(); i++)
    {
        if((s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z')) {
            res += s[i];
        }
        else if(s[i] == '(') {
            st.push(s[i]);
        }
        else if(s[i] == ')') {
            while (!st.empty() && st.top() != '(')
            {
                res += st.top();
                st.pop();
            }
            if(!st.empty()) {
                st.pop(); // Popping '(' here
            }
        }
        else {
            while (!st.empty() && prec(st.top()) >= prec(s[i]))
            {
                res += st.top();
                st.pop();
            }
            st.push(s[i]);
        }
    }
    
    while (!st.empty())
    {
       res += st.top();
       st.pop();
    }
    
    return res;
}

int main() {
    string exp = "a+b*(c^d-e)^(f+g*h)-i";
    cout<<infixToPostfix(exp);
    return 0;
}

python postfix conversion

"""
Author : ITVoyagers (itvoyagers.in)

Date :31st October 2019

Description : Program to show use of stack in infix to postfix conversion using python.
"""
class infix_to_postfix:
    precedence={'^':5,'*':4,'/':4,'+':3,'-':3,'(':2,')':1}
    def __init__(self):
        self.items=[]
        self.size=-1
    def push(self,value):
        self.items.append(value)
        self.size+=1
    def pop(self):
        if self.isempty():
            return 0
        else:
            self.size-=1
            return self.items.pop()
    def isempty(self):
        if(self.size==-1):
            return True
        else:
            return False
    def seek(self):
        if self.isempty():
            return false
        else:
            return self.items[self.size]
    def isOperand(self,i):
        if i in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ':
            return True
        else:
            return False
    def infixtopostfix (self,expr):
        postfix=""
        print('postfix expression after every iteration is:')
        for i in expr:
            if(len(expr)%2==0):
                print("Incorrect infix expr")
                return False
            elif(self.isOperand(i)):
                postfix +=i
            elif(i in '+-*/^'):
                while(len(self.items)and self.precedence[i]<=self.precedence[self.seek()]):
                    postfix+=self.pop()
                self.push(i)
            elif i is '(':
                self.push(i)
            elif i is ')':
                o=self.pop()
                while o!='(':
                    postfix +=o
                    o=self.pop()
            print(postfix)
                #end of for
        while len(self.items):
            if(self.seek()=='('):
                self.pop()
            else:
                postfix+=self.pop()
        return postfix
s=infix_to_postfix()
expr=input('enter the expression ')
result=s.infixtopostfix(expr)
if (result!=False):
    print("the postfix expr of :",expr,"is",result)