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Thread: EVALUATION OF POSTFIX NOTATION

  1. #1
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    Default EVALUATION OF POSTFIX NOTATION

    class StackObj
    {
    private Object[] theStack;
    private int maxSize;
    private int top;

    public StackObj(int s)
    {
    maxSize = s;
    theStack = new Object[maxSize];
    top = -1;
    }
    public void push(Object elem)
    {
    top++;
    theStack[top] = elem;
    }
    public Object pop()
    {
    Object result = theStack[top];
    top--;
    return result;
    }
    public Object top()
    {
    return theStack[top];
    }
    public boolean isFull()
    {
    return (top == (maxSize-1) );
    }
    public boolean isEmpty()
    {
    return (top == -1);
    }
    public int size()
    {
    return (top+1);
    }
    }

    Ok so this is a class called STACKOBJ that is a stack of OBJECTS...
    THIS IS THE CODE...
    [CENTER]public static int evaluatepostfix(String S){
    		StackObj temp = new StackObj(S.length());
    		for(int i = 0; i < S.length(); i++){
    			if(((Integer.parseInt(S.charAt(i) + "")) >= 1) && ((Integer.parseInt(S.charAt(i) + "")) <= 9)){
    				temp.push(new Integer (Integer.parseInt((S.charAt(i)+"")))); 
    				break;
    			}else{
    				int op1 = ((Integer)temp.pop()).intValue();
    				int op2 = ((Integer)temp.pop()).intValue();
    				switch (S.charAt(i)){
    					case '+': temp.push(new Integer ((op2) + (op1))); break;
    					case '-': temp.push(new Integer ((op2) - (op1))); break;
    					case '*': temp.push(new Integer ((op2) * (op1))); break;
    					case '/': temp.push(new Integer ((op2) / (op1))); break;	
    				}
    			}
    		}
    		return ((Integer)temp.pop()).intValue();
    	}[/CENTER]
    Apparently if I try to run System.out.print(evaluatepostfix("123*+9-")); the output is 1 :S
    HELP???


  2. #2
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    Default Re: EVALUATION OF POSTFIX NOTATION

    if(((Integer.parseInt(S.charAt(i) + "")) >= 1) && ((Integer.parseInt(S.charAt(i) + "")) <= 9)){
        temp.push(new Integer (Integer.parseInt((S.charAt(i)+"")))); 
        break; // ?????
    Think very carefully what that statement does. When you fix that you will have plenty of other problems to fix.
    Improving the world one idiot at a time!

  3. The Following User Says Thank You to Junky For This Useful Post:

    Medo Almasry (November 7th, 2011)

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    Default Re: EVALUATION OF POSTFIX NOTATION

    all this means is that if the character is between 1 and 9 push it into the stack...

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    Default Re: EVALUATION OF POSTFIX NOTATION

    No. I'm talking about the break statement. What does that do?
    Improving the world one idiot at a time!

  6. #5
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    Default Re: EVALUATION OF POSTFIX NOTATION

    I guess this is what happens when you spend hours watching the big bang theory -.-
    THANKS ALOT MAN
    I missed out that one

  7. #6
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    Default Re: EVALUATION OF POSTFIX NOTATION

    Your next assignment should you choose to accept is to write a game for Rock, Paper, Scissors, Lizard, Spock.
    Improving the world one idiot at a time!

  8. #7
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    Default Re: EVALUATION OF POSTFIX NOTATION

    I shall respectfully reject the offer because right now am working on databases (stacks, queues, linked lists, trees)...
    and regarding games, next semester I shall be taking GUI and most probably I will be doing Entanglement *its a game*...
    Thanks again for the offer and if you have a source for questions that could make me better... a website or a book... that would be great...
    If you are wondering, I'm a computer Programmer "YET TO BE :p" but am just having a burnout here...

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