Answers for "infix to postfix conversion in compiler design"

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;
}

infix to postfix conversion c++

//Easiet way to solve infix to postfix expression
bool isOperator(char c)
{
	if(c=='+'||c=='-'||c=='*'||c=='/'||c=='^')
	{
		return true;
	}
	else
	{
		return false;
	}
}

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(stack<char> s, string infix)
{
	string postfix;
	for(int i=0;i<infix.length();i++)
	{
		if((infix[i] >= 'a' && infix[i] <= 'z')
		||(infix[i] >= 'A' && infix[i] <= 'Z'))
		{
			postfix+=infix[i];
		}
		else if(infix[i] == '(')
		{
			s.push(infix[i]);
		}
		else if(infix[i] == ')')
		{
			while((s.top()!='(') && (!s.empty()))
			{
				char temp=s.top();
				postfix+=temp;
				s.pop();
			}
			if(s.top()=='(')
			{
				s.pop();
			}
		}
		else if(isOperator(infix[i]))
		{
			if(s.empty())
			{
				s.push(infix[i]);
			}
			else
			{
				if(precedence(infix[i])>precedence(s.top()))
				{
					s.push(infix[i]);
				}	
				else if((precedence(infix[i])==precedence(s.top()))&&(infix[i]=='^'))
				{
					s.push(infix[i]);
				}
				else
				{
					while((!s.empty())&&( precedence(infix[i])<=precedence(s.top())))
					{
						postfix+=s.top();
						s.pop();
					}
					s.push(infix[i]);
				}
			}
		}
	}
	while(!s.empty())
	{
		postfix+=s.top();
		s.pop();
	}
	
	return postfix;
}

int main() 
{  

  	string infix_exp, postfix_exp;
  	cout<<"Enter a Infix Expression :"<<endl;
  	cin>>infix_exp;
  	stack <char> stack;
	cout<<"INFIX EXPRESSION: "<<infix_exp<<endl;
  	postfix_exp = InfixToPostfix(stack, infix_exp);
  	cout<<endl<<"POSTFIX EXPRESSION: "<<postfix_exp;
	  
	return 0;
}