Infix to postfix algorithm

[Torvald Helmer]

I need help to finish my agorithm!
This is what I have so far:

import java.util.Stack;
import javax.swing.*;
 
public class InfixToPostfix  {
 
     public static void main(String[] args)  {
 
     Object slutt = "#";
     char[] operator = {'^','*','/','+','-'};
     char vParentes = '(';
     char hParentes = ')';
     char[] uOperator = {'^','*','/','+','-','('};
 
     char[] opPri = {'^','*','/','+','-','(',')','#'};
     int [] infixPri = { 3 , 2 , 2 , 1 , 1 , 4 , 0 , 0 };
     int [] opStackPri = { 3 , 2 , 2 , 1 , 1 , 0 ,-1 , 0 };
 
     String infixStr = JOptionPane.showInputDialog("infix : ");
     infixStr += slutt;
     String postfixStr = "";
 
     System.out.println("Infix: "+infixStr);
 
     Stack stack = new Stack();
     System.out.println ("Stack is empty: "+stack.empty ());
 
     char c;
 
     for (int i=0; i<infixStr.length(); i++)  {
          c = infixStr.charAt(i);
 
          if (c == '+' || c == '-' || c == '*' || c == '/')  {  
               if (stack.empty())  {
               stack.push(String.valueOf(c));
               }
               else  {
                    // HELP WANTED!!!!!
               }
          }
          else if (c == '#')  {
                System.out.println("Postfix: "+ postfixStr);
                System.exit(0);
          }
          else  {
                postfixStr += c;
          }
      }
   }
}

In the "help wanted" else-loop I want to do the following:

The operator from stack should pop, and
it must be compared with the next operator
from the infix-expression, in according to the
priority which is given in the opPri, infixPri and opStackPri.
The if the infix-operator has a higher priority then I push it
to the stack, else the stack-operator pops and are added
to the postfix-string, and the next stack operator is popped and
compared with the same infix-operator. Then again if the infix has
a higher value I push it to the stack, else the stack-operator is popped
and added. So on and so on...

And it's only supposed to handle one digits numbers.

As you see, I know how it should function, but I am not sure at all
about the syntax. Can anyone please help me with this?

thanks!

torvald helmer

[Ernest Friedman-Hill]

Hi,

Welcome to JavaRanch!

Please post your questions to one and only one forum. See here for an explanation. I've deleted the other two copies of this that you posted.