Question

Write a program that will take a string, parse it, and then calculate the value in post-fix (reverse polish) notation. To understand this mostly every expression you’ve seen in math is called in-fix notation.

In-fix Example:
3 + 2
However in post-fix notation the operator is at the end of the expression.
Post-fix Example:
3 2 +

Answer 1

Answer and Step-by-step explanation:

/**POSTFIX CALCULATION IN JAVA ****/

import java.io.*;

import java.util.*;

import java.lang.*;

public class ReversePolishIMP

{

//main

public static void main(String[] args)

{

//DECLARE VARIABLE

int opnd1;

int opnd2;

int rst=0;

//SCANNER TO READ POSTFIX STRING

Scanner revScan=new Scanner(System.in);

String postFix;

//ASK REPEATEDLY

while(true)

{

System.out.println("Enter a reverse polish expressio nor quit to quit");

postFix=revScan.nextLine();

//CHAECK FOR PROGRAM quit

if(postFix.equals("quit"))

{

System.out.println("Goodbye");

break;

}

//CREATE STACK TO STORE OPERANDS

Stack<String> stringStack=new Stack<String>();

//SPLIT THE STRING

String[] t = postFix.split(" ");

//PROCESS POSTFIX

for(int k = 0; k < t.length; k++)

{

String tok = t[k];

//FIND OPERAND

if (!"+".equals(tok) && !"*".equals(tok) && !"-".equals(tok) && !"/".equals(tok))

stringStack.push(tok);

else

{

//PERFORM ADDITION, SUBTRACTION,MULTIPLICCATION,DIVISION

String calOptr = t[k];

opnd1 = Integer.parseInt(stringStack.pop());

opnd2 = Integer.parseInt(stringStack.pop());

if (calOptr.equals("/"))

rst = opnd1 / opnd2;

else if(calOptr.equals("*"))

rst = opnd1 * opnd2;

else if(calOptr.equals("+"))

rst = opnd1 + opnd2;

else if(calOptr.equals("-"))

rst = opnd2 - opnd1;

else System.out.println("Illeagal symbol");

//STORE RESULT IN STACK

stringStack.push(Integer.toString(rst));

}

}

//GET FINAL RESULT

rst=Integer.parseInt(stringStack.pop());

//CHECK FOR EMPTY STACK

if(!stringStack.isEmpty())

{

System.out.println("THIS WAS NOT PROPERLY FORMATTED");

System.out.println("0");

}

else

System.out.println(rst);

}

}

}