Question

Write a java program to convert and print an infix expression to postfix expression. You can use Java stack methods. (Must read input from System.in)

Your main method should be as follow:

public static void main(String args[]) {

intopost p = new intopost ();

String iexp, pexp; //infix postfix expression            

try{

Scanner inf = new Scanner (System.in);                    

// Read input from KB/ File

while(inf.hasNext()){

// read next infix expression                                

iexp = inf.next();

// Assume method name to convert infix to postfix is postfix

pexp = p.postfix(iexp);

System.out.printf("\nPosfix of %s is: %s", iexp, pexp);

}// end while

inf.close();// close input file

}catch (Exception e) {prt("\nException " + e + "\n");}

} //end main method

Answer 1

import java.util.Scanner;

import java.util.Stack;

class intopost {

int precedence(char ch)

{

switch (ch)

{

case '+':

case '-':

return 1;

case '*':

case '/':

return 2;

case '^':

return 3;

}

return -1;

}

public String postfix(String exp)

{

String result = new String("");

  

Stack<Character> stack = new Stack<>();

  

for (int i = 0; i<exp.length(); ++i)

{

char c = exp.charAt(i);

if (Character.isLetterOrDigit(c))

result += c;

else if (c == '(')

stack.push(c);

else if (c == ')')

{

while (!stack.isEmpty() && stack.peek() != '(')

result += stack.pop();

  

if (!stack.isEmpty() && stack.peek() != '(')

return "Invalid Expression"; // invalid expression

else

stack.pop();

}

else {

while (!stack.isEmpty() && precedence(c) <= precedence(stack.peek())) {

if(stack.peek() == '(')

throw new IllegalArgumentException("Invalid exprssion!!");

result += stack.pop();

   }

stack.push(c);

}

}

// pop all the operators from the stack

while (!stack.isEmpty()){

if(stack.peek() == '(')

return "Invalid Expression";

result += stack.pop();

   }

return result;

}

}

public class Main {

public static void main(String args[]) {

intopost p = new intopost ();

String iexp, pexp; //infix postfix expression

try{

Scanner inf = new Scanner(System.in);

// Read input from KB/ File

while(inf.hasNext()){

// read next infix expression

iexp = inf.next();

// Assume method name to convert infix to postfix is postfix

pexp = p.postfix(iexp);

System.out.printf("\nPosfix of %s is: %s", iexp, pexp);

}// end while

inf.close();// close input file

}catch (Exception e) {

System.out.println("\nException " + e + "\n");}

} //end main method

}

1e import java.util.Scanner; 2 import java.util.Stack; 4 class intopost { int precedence(char ch) switch (ch) 800 von case '+': case '-': return 1; case '': case '/' : return 2; case 'A': return 3; return -1; Problems @ Javadoc Declaration Search Console X - Prog Main (2) (Java Application) /Library/Java/JavaVirtual Machines/jdk1.8.0_144.jdk/Con a+b*(cd-e)^(f+g*h)-i Posfix of a+b'(cd-e)(f+g*h)-i is: abcdefgh*+^*+i-