This is an infix to postfix converter using java. This is what I have done so fa

ID: 3774384 • Letter: T

Question

This is an infix to postfix converter using java. This is what I have done so far and it won't run after inputting my infix expression. This is the error I get,

Exception in thread "main" java.util.EmptyStackException
at java.util.Stack.peek(Unknown Source)
at java.util.Stack.pop(Unknown Source)
at InToPost.convert(InToPost.java:62)
at InToPost.main(InToPost.java:103)

My code:

import java.util.Scanner;
import java.util.Stack;

public class InToPost
{
public static boolean isLetterOrNumber(char ch)
{
  if (ch >= '0' && ch <= '9')
  {
   return true;
  }
  else if (ch >= 'a' && ch <= 'z')
  {
   return true;
  }
  else if (ch >= 'A' && ch <= 'Z')
  {
   return true;
  }
  else
   return false;
}
public static boolean isLowerPrecedence(char op1, char op2)
    {
        if (op1 == '+' || op1 == '-')
        {
        return !(op2 == '+' || op2 == '-');
        }
        else if (op1 == '*' || op1 == '/')
        {
        return op2 == '^' || op2 == '(';
        }
        else if (op1 == '^')
        {
        return op2 == '(';
        }
        else if (op1 == '(')
        {
        return true;
        }
        else
        {
        return false;
        }
    }
public static String convert(String infix)
{
  Stack<Character> stack = new Stack<Character>();
  String postfix = "";
  int infixLength = infix.length();
  for (int i = 0; i < infixLength; i++)
  {
   if(infix.charAt(i) == ' ' || infix.charAt(i) == ',')
   {
    continue;
   }
   else if(isLetterOrNumber(infix.charAt(i)))
   {
    while(!stack.isEmpty() && stack.pop() != '('
      && isLowerPrecedence(stack.pop(), infix.charAt(i)));
    {
     postfix += stack.pop();
     stack.pop();
    }
    stack.push(infix.charAt(i));
   }
   else if(isLetterOrNumber(infix.charAt(i)))
   {
    postfix += infix.charAt(i);
   }
   else if (infix.charAt(i) == '(')
   {
    stack.push(infix.charAt(i));
   }
   else if(infix.charAt(i) == ')')
   {
    while(!stack.isEmpty() && stack.pop() != '(')
    {
     postfix += stack.pop();
     stack.pop();
    }
    stack.pop();
   }
  }
  while(!stack.isEmpty())
  {
   postfix += stack.pop();
   stack.pop();
  }
  return postfix;
}
public static void main(String args[])
{
   // create a new scanner for user input
  Scanner keyboard = new Scanner(System.in);
   // new string for user input of infix notation expression
  String infix;
   // prompts the user for an input
  System.out.println("Enter an expression in infix form: ");
   // takes the input and sets it too variable String infix
  infix = keyboard.next();
   // output given infix notation
  System.out.println("Expression in Infix Notation: " + infix);
   // sets a new string variable postfix after calling the convert method
   // to convert infix input to postfix
  String postfix = convert(infix);
   // outputs the new postfix expression
  System.out.println("Expression in Postfix Notation: " + postfix);
}
}

Explanation / Answer

import java.util.Scanner;
import java.util.Stack;
public class HelloWorld{

public static boolean isOperator(char c)
{
return c == '+' || c == '-' || c == '*' || c == '/' || c == '^'
|| c == '(' || c == ')';
}

public static boolean isLowerPrecedence(char op1, char op2)
{
switch (op1)
{
case '+':
case '-':
return !(op2 == '+' || op2 == '-');

case '*':
case '/':
return op2 == '^' || op2 == '(';

case '^':
return op2 == '(';

case '(':
return true;

default:
return false;
}
}
public static String convert(String infix)
{Stack<Character> stack = new Stack<Character>();
StringBuffer postfix = new StringBuffer(infix.length());
char c;

for (int i = 0; i < infix.length(); i++)
{
c = infix.charAt(i);

if (!isOperator(c))
{
postfix.append(c);
}

else
{
if (c == ')')
{

while (!stack.isEmpty() && stack.peek() != '(')
{
postfix.append(stack.pop());
}
if (!stack.isEmpty())
{
stack.pop();
}
}

else
{
if (!stack.isEmpty() && !isLowerPrecedence(c, stack.peek()))
{
stack.push(c);
}
else
{
while (!stack.isEmpty() && isLowerPrecedence(c, stack.peek()))
{
Character pop = stack.pop();
if (c != '(')
{
postfix.append(pop);
} else {
c = pop;
}
}
stack.push(c);
}

}
}
}
while (!stack.isEmpty()) {
postfix.append(stack.pop());
}

return postfix.toString();
}

public static void main(String args[])
{
// create a new scanner for user input
Scanner keyboard = new Scanner(System.in);
// new string for user input of infix notation expression
String infix;
// prompts the user for an input
System.out.println("Enter an expression in infix form: ");
// takes the input and sets it too variable String infix
infix = keyboard.next();
// output given infix notation
System.out.println("Expression in Infix Notation: " + infix);
// sets a new string variable postfix after calling the convert method
// to convert infix input to postfix
String postfix = convert(infix);
// outputs the new postfix expression
System.out.println("Expression in Postfix Notation: " + postfix);
}
}

*******OUTPUT**********

Enter an expression in infix form:

a+b

Expression in Infix Notation: a+b

Expression in Postfix Notation: ab+

*******OUTPUT***********

Navigate

This is an individuel assigrment check Blackboard for the due deles: Before you

This is an inflate and deflate exercise using the Consumer Price Index, which ca

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.

This is an infix to postfix converter using java. This is what I have done so fa

Question

Explanation / Answer

Related Questions

Navigate