Thread: need help converting from infix to postfix notation

Originally Posted by Norm

Do you have an algorithm/design for what you are trying to do? What are the steps in the algorithm that you are having problems coding.

Can you post the program's output and explain what is wrong with it?

The posted code does not compile because it is missing the import statements.

mine does have the import statements, I just forgot to put them in the post. The problem with my output is that I'm only printing the numbers out, I can't figure out why I'm not displaying the operators

input 1 + 2

run:
1 2 BUILD SUCCESSFUL (total time: 0 seconds)

look at the code above I made a small mod in the main method in the else statement there's a System.out.print that it wasn't before....

Originally Posted by Norm

Sorry, I can't do anything without a version that compiles, executes and shows the problems.

Here are the other two classes needed for this program, and you should have a text file datafile.txt with a simple expression like 1 + 2 $

package postfixstack;
 
public class Node<T> {
 
    T value;
    Node next;
 
    //constructor
    public Node(T a)
    {
        value = a;
        next = null;
    }    
}

package postfixstack;
 
 
public class Stack<T> {
 
    public Node<T> head;
 
    //constructor
    public Stack()
    {
        head = null;
    }
 
    //adding to stack
    public void push(T a)
    {
        Node p = new Node(a);
        p.next = head;
        head = p;
    }
 
    //removing from stack
    public void pop()
    {
        head = head.next;
    }
 
    //getting top element
    public T top()
    {
        return head.value;
    }
 
    public boolean isEmpty()
    {
        return head == null;
    }
 
    //dispaly stack
    public void display()
    {
        if(head == null)
            System.out.println("Stack is empty!...");
        else
        {
            Node s = head;
            while(s != null)
            {
                System.out.println(s.value);
                s = s.next;
            }
        }
    }
 
    //checking for operators
    public boolean isOperator(String s)
    {
        String operator = "-+*/^()";
        if(operator.indexOf(s) != -1)
            return true;
        else
            return false;
    }
 
    //returning level of priority
    public int priority(String s)
    {
        if(s.equals("-") || s.equals("+"))
            return 1;
        if(s.equals("*") || s.equals("/"))
            return 2;
        else
            return 3;       
    }
 
    //return associativity (left or right)
    public String associativity(int level)
    {               
        if(level <= 2)
            return "left";
        else
            return "right";            
    }
 
}

Originally Posted by Norm

Also posted at need help converting from infix to postfix notation

Thanks man!... I got it working! you've been very helpful

cheers