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Thread: What does this code output?

  1. #1
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    Question What does this code output?

    I can't seems to get the output of this code to display in the console window, evening after implementing a System.out.println() for each variable. Could someone give me some suggestion or possible output for the code, thanks.

     public class Evaluate
    {
    public static void main(String[] args)
    {
    Stack<String> ops = new Stack<String>();
    Stack<Double> vals = new Stack<Double>();
    while (!StdIn.isEmpty())
    { // Read token, push if operator.
    String s = StdIn.readString();
    if (s.equals("(")) ;
    else if (s.equals("+")) ops.push(s);
    else if (s.equals("-")) ops.push(s);
    else if (s.equals("*")) ops.push(s);
    else if (s.equals("/")) ops.push(s);
    else if (s.equals("sqrt")) ops.push(s);
    else if (s.equals(")"))
    { // Pop, evaluate, and push result if token is ")".
    String op = ops.pop();
    double v = vals.pop();
    if (op.equals("+")) v = vals.pop() + v;
    else if (op.equals("-")) v = vals.pop() - v;
    else if (op.equals("*")) v = vals.pop() * v;
    else if (op.equals("/")) v = vals.pop() / v;
    else if (op.equals("sqrt")) v = Math.sqrt(v);
    vals.push(v);
    } // Token not operator or paren: push double value.
    else vals.push(Double.parseDouble(s));
    }
    StdOut.println(vals.pop());
    }
    }
    Last edited by helloworld922; January 14th, 2012 at 01:37 PM.


  2. #2
    Administrator copeg's Avatar
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    Default Re: What does this code output?

    These forums don't work like that. Perhaps you should be getting to the root of the problem - like why you see no output (does it compile?) - rather than asking someone to do your work for you

  3. #3
    Super Moderator helloworld922's Avatar
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    Default Re: What does this code output?

    Step 1: Format your code to be easily readable (i.e. add tabs).

    Step 2: What issue are you running into specifically? Compiler errors? Runtime errors? Which ones?

    fyi, StdOut and StdIn are not defined by default in Java, use System.out and System.in instead.

  4. #4
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    Default Re: What does this code output?

    Quote Originally Posted by copeg View Post
    These forums don't work like that. Perhaps you should be getting to the root of the problem - like why you see no output (does it compile?) - rather than asking someone to do your work for you

    That what I really meant to ask? I tried compiling this program several times but did't see any output. So, copeg or anyone could you give me any suggestion on why I'm not seeing any output when I run this code. Hey, I any revise it a little to showing that I am really putting effort into this. Here is the revise version:
    import java.io.BufferedInputStream;
    import java.lang.*;
    import java.util.*;
    import java.util.Scanner;
    import java.io.PrintWriter;
    import java.io.UnsupportedEncodingException;
    import java.util.Locale;
     
     
    public class StdIn {
     
    	 private static Scanner scanner = new Scanner(new BufferedInputStream(System.in));
     
     
    	 public static boolean isEmpty() {
    	        return !scanner.hasNext();
    	    }
     
    	 public static String readString() {
    	        return scanner.next();
    	    }
     
     
     
    	public  static void main (String args[]){ 
     
     
    		//InputStreamReader input = new InputStreamReader(System.in);
    		//BufferedReader reader = new BufferedReader(input);
     
    		Stack<String> ops = new Stack<String>();
     
    		Stack<Double> vals = new Stack<Double>();
    		//String s = reader.readLine();
     
     
     
    		while (!StdIn.isEmpty())
    		{ // Read token, push if operator.
    			String s = StdIn.readString();
    		if (s.equals("(")) ;
    		else if (s.equals("+")) ops.push(s);
    		else if (s.equals("-")) ops.push(s);
    		else if (s.equals("*")) ops.push(s);
    		else if (s.equals("/")) ops.push(s);
    		else if (s.equals("sqrt")) ops.push(s);
    		else if (s.equals(")"))
     
    		{ // Pop, evaluate, and push result if token is ")".
    		String op = ops.pop();
    		double v = vals.pop();
    		if (op.equals("+")) v = vals.pop() + v;
    		else if (op.equals("-")) v = vals.pop() - v;
    		else if (op.equals("*")) v = vals.pop() * v;
    		else if (op.equals("/")) v = vals.pop() / v;
    		else if (op.equals("sqrt")) v = Math.sqrt(v);
    		vals.push(v);
    		System.out.println(vals.push(v));
    		} // Token not operator or paren: push double value.
    		else vals.push(Double.parseDouble(s));
    		System.out.println(Double.parseDouble(s));
     
    		}
    		System.out.println(vals.pop());	
     
     
     
    	}
     
     
     
     
     
    	}
    Last edited by helloworld922; January 15th, 2012 at 04:46 PM.

  5. #5
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    Default Re: What does this code output?

    The current issue I am having with this code is: figuring out why don't I see any output. I take some of your suggestion: Here is a revise version of my code:
              //import java.io.*;
    	//import java.math.*;
    	//import java.io.OutputStreamWriter;
    	import java.io.BufferedInputStream;
    	//import java.lang.*;
    	import java.util.*;
    	import java.util.Scanner;
    	//import java.io.PrintWriter;
    	//import java.io.UnsupportedEncodingException;
    	//import java.util.Locale;
     
     
    	public class StdIn {
     
    	private static Scanner scanner = new Scanner(new BufferedInputStream(System.in));
     
     
    	 public static boolean isEmpty() 
    		 { return !scanner.hasNext();}
     
     
    	 public static String readString() 
    		 { return scanner.next();}
     
     
     
    	public  static void main (String args[]){ 
     
     
    	Stack<String> ops = new Stack<String>();
     
    	Stack<Double> vals = new Stack<Double>();
     
     
     
    	while (!StdIn.isEmpty())
    	{ // Read token, push if operator.
    		String s = StdIn.readString();
    	if (s.equals("(")) ;
    	else if (s.equals("+")) ops.push(s);
    	else if (s.equals("-")) ops.push(s);
    	else if (s.equals("*")) ops.push(s);
    	else if (s.equals("/")) ops.push(s);
    	else if (s.equals("sqrt")) ops.push(s);
    	else if (s.equals(")"))
     
    	{ // Pop, evaluate, and push result if token is ")".
    	String op = ops.pop();
    	double v = vals.pop();
    	if (op.equals("+")) v = vals.pop() + v;
    	else if (op.equals("-")) v = vals.pop() - v;
    	else if (op.equals("*")) v = vals.pop() * v;
    	else if (op.equals("/")) v = vals.pop() / v;
    	else if (op.equals("sqrt")) v = Math.sqrt(v);
    	vals.push(v);
    	System.out.println(vals.push(v));
    	} // Token not operator or paren: push double value.
    	else vals.push(Double.parseDouble(s));
    	System.out.println(Double.parseDouble(s));
     
    	}
    	System.out.println(vals.pop());	
     
     
    	}
     
     
    	}
    Last edited by helloworld922; January 15th, 2012 at 04:47 PM.

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