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Thread: [Help]Reverse Polish Notation

  1. #1
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    Question [Help]Reverse Polish Notation

    Hello, I've been working on this for weeks now and I'm still not getting it. It works fine with two numbers but any more than that and it'll crash or return the wrong value. Please check my code and let me know what I can do to fix it. I can only use stacks and queues. I also have a menu and driver but I don't know if that's needed. My assignment is basically to use scanner to look for input values and operators and then solve it. It's only single digits and I'm supposed to be able to input as many digits and operators as I want and the code should still be able to solve it. Please help!

    public class ReversePolishNotation
    {
        Queue <String> myQueue;
        public ReversePolishNotation()
        {
            myQueue = new LinkedList <String>();
        }
     
        public void doMath()
        {
            Stack <Integer> myStack = new Stack <Integer>();
            Queue <String> sign = new LinkedList <String>();
            Scanner console = new Scanner(System.in);
            int second;
            int first;
     
            while(console.hasNextInt())
            {
                myStack.push(console.nextInt());
            }
            while(console.hasNextLine() && !(console.nextLine()).equals("q"))
            {
                sign.add(console.nextLine());
            }
     
            String operator = sign.remove();
            second = myStack.pop();
            first = myStack.pop();
            do
            {
                if(operator.equals("+"))
                {
                    int result = second+first;
                    myStack.push(result);
                    myQueue.add(first + "+" + second + "=" + result);
                    if(!sign.isEmpty())
                    {
                        operator = sign.remove();
                        second = myStack.pop();
                        first = myStack.pop();
                    }
                }
                else if(operator.equals("-"))
                {
                    int result = first-second;
                    myStack.push(result);
                    myQueue.add(first + "-" + second + "=" + result);
                    if(!sign.isEmpty())
                    {
                        operator = sign.remove();
                        second = myStack.pop();
                        first = myStack.pop();
                    }
                }
                else if(operator.equals("*"))
                {
                    int result = second*first;
                    myStack.push(result);
                    myQueue.add(first + "*" + second + "=" + result);
                    if(!sign.isEmpty())
                    {
                        operator = sign.remove();
                        second = myStack.pop();
                        first = myStack.pop();
                    }
                }
                else
                {
                    int result = first/second;
                    myStack.push(result);
                    myQueue.add(first + "/" + second + "=" + result);
                    if(!sign.isEmpty())
                    {
                        operator = sign.remove();
                        second = myStack.pop();
                        first = myStack.pop();
                    }
                }
            }
            while(!sign.isEmpty());
        }
    }
    Last edited by Cluelesscoder; May 20th, 2014 at 10:21 PM.


  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: Reverse Polish Notation

    What is this code supposed to do? What Exception does it throw? For what input? What line is the Exception on?
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  3. #3
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    Default Re: Reverse Polish Notation

    Quote Originally Posted by KevinWorkman View Post
    What is this code supposed to do? What Exception does it throw? For what input? What line is the Exception on?
    It's supposed to solve math problems postfix. So if I input 9 5 -, it'll return 4. If i input 8 4 7 + -, it'll return -3. There aren't any exceptions, not that I know of. It's just not working with any more than 2 numbers. I tried to find the problem earlier and apparently, it's not taking in all of the values that I'm inputting. the Queue only takes in every other line, I think.

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    Default Re: Reverse Polish Notation

    Okay, so I've been working on the code and I realized a huge problem is that sign and myStack aren't taking in the values properly. Can someone please fix it. Write a short code that let's sign and myStack take in numbers and operators correctly.

    Also, for clarification, sign is supposed to take in the plus and minus signs while myStack is supposed to take in the numbers.

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    Default Re: [Help]Reverse Polish Notation

    No, we won't fix it for you or write code to order.

    Continue your debugging to determine why the tokens aren't being 'stacked' properly.

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