ItoP2

package bubs;

import java.util.*;
import java.io.*;

public class ItoP { // infix to postfix
	int prec(char c) {
		//it gives precedence of mathematical operator like bodmas rule
		if(c=='^') {
			return 3; //highest precedence
		}
		else if(c=='/' || c =='*') {
			return 2;
		}
		else if(c == '+' || c =='-') {
			return 1;
		}
		else {
			return -1;
		}
	}
	
	String Infixtopostfix(String f){
		
		String output = ""; //postfix string
		String s= "";
		Stack<String> op = new Stack<String>();
		char c;
		char ch;
		String fix = f;
		String postfix = "";
		for(int i=0;i<fix.length();i++) {
			c = fix.charAt(i);
			if(c != '+' && c != '-' && c != '%'&& c != '/' && c != '+'&& c != '*' && c != '+'&& c != '(' && c != ')') {
				postfix = postfix + c;
			}
			// if operator is scanned
			else if(c == '+' || c == '-' || c == '%'|| c == '/' || c == '+'|| c == '*' || c == '+'|| c == '(' || c == ')') {
				//logic with precedence
				//op.push(c+"");
				while(!op.isEmpty() && prec(c) < prec(op.peek())) {
					output = output + op.pop();
				}
				op.push(c);
			}	
			else if(c == ')') {
				ch=op.pop(); //take out top element from stack
				if(!ch.equals('(')) {
					output = output + s;
				}
			}
			else {
				System.out.println("khali hai");
			}
		}
		System.out.println("Output :"+output);
		return output;
	}
	
	public static void main(String[] args) {
		
		ItoP p = new ItoP();
		try {
			Scanner sc = new Scanner(System.in);
			String expression = sc.nextLine();
			String postfix = p.Infixtopostfix(expression);
			System.out.println("The postfix expression is :"+postfix);
		}
		catch(Exception e) {
			e.printStackTrace();
		}
	}
}