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Thread: How do I do this, code supplied

  1. #1
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    Default How do I do this, code supplied

    Hey I am doing a tutorial at uni and I need to write a code that

    Task 3
    Write a program that accept from the command line number n and then print stars * in n rows.
    For example, if n = 5 then the program should print:
    *
    * *
    * * *
    * * * *
    * * * * *
    Note that you must let the user input the number for rows from the command line. For example, if the command line input is 5, you will have args[0] = "5". Then you can use
    int n = Integer.parseInt(args[0]); // now n=5

    here is my code so far, I have asked my tutorial teacher. All she did was pass me a pen and paper and smile and there is nothing in the lectures about how to do it. Any help, as quick as possible would be appreciated.

    public class ArgsLoop {
    public static void main(String[] args) {
    int n = Integer.parseInt(args[0]); // now n=5
    for(int i=0;r<n;i++){
    System.out.println("*");
    for(int c=i; c<n; c++){
    System.out.print("*");
    }
    }
    }
    }


  2. #2
    Super Moderator jps's Avatar
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    Default Re: How do I do this, code supplied

    for(int i = 0; r < n; i++) {
    Where does the 'r' come from?

    Please use code tags when posting code, help can be found here

  3. #3
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    Default Re: How do I do this, code supplied

    public class ArgsLoop {
    	public static void main(String[] args) {
    	int n = Integer.parseInt(args[0]); // now n=5
    		for(int i=1;i<n;i++){
    			System.out.println("*");
    			for(int c=0; c<i; c++){
    				System.out.print("*");
    			}
    			}
    		}
    	}

    i is suppose to be the rows, c is the columns I've been working on it a bit, it comes up with the result

    *
    **
    ***
    ****
    ****
    now

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    Senior Member PhHein's Avatar
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    Default Re: How do I do this, code supplied

    You have to seperate the line breaks from the output of the *.
    The two nested loops are a good start. Do it again with paper and pencil and find out how often each loop should run.

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    Default Re: How do I do this, code supplied

    That's not helping ^. Can you show me how to do it in code, don't you think I have used paper and pen? That's exactly what I wrote in my first post.
    I have been playing around with this code for hours, I know it's something simple. But that is really not helping it at all. I already have the second loop to set up to not write lines.

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    Default Re: How do I do this, code supplied

    Then your pencil is broken! Your outer loop only runs four times. I will not provide any code, that's your task. I'll only give, in your perception, unhelpful advice.

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    Default Re: How do I do this, code supplied

    for(int i=0;i<n;i++){
    System.out.println("*");

    I fixed the outer loop,
    it runs five times now, but the inner loop still isn't working

  8. #8
    Senior Member PhHein's Avatar
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    Default Re: How do I do this, code supplied

    As I cannot see your inner loop, it's hard to tell. Please always post your complete code, so that members see your actual version.

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    Default Re: How do I do this, code supplied

    public class ArgsLoop {
    	public static void main(String[] args) {
    	int n = Integer.parseInt(args[0]); // now n=5
    		for(int i=0;i<n;i++){
    			System.out.println("*");
    			for(int c=i; c>-1; c--){
    				System.out.print("*");
    			}
    		}
    	}
    }

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    Default Re: How do I do this, code supplied

    Quote Originally Posted by MooseManX View Post
    but the inner loop still isn't working
    ...and describe what isn't working means.

  11. #11
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    Default Re: How do I do this, code supplied

    it is posting an extra line e.g

    *
    **
    ***
    ****
    *****
    *****
    that's my output now

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    Default Re: How do I do this, code supplied

    From my earlier reply
    You have to seperate the line breaks from the output of the *.

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    Default Re: How do I do this, code supplied

    public class ArgsLoop {
    	public static void main(String[] args) {
    	int n = Integer.parseInt(args[0]); // now n=5
    		for(int i=0;i<n;i++){
    			System.out.println();
    			System.out.print("*");
    			for(int c=i-1; c>-1; c--){
    				System.out.print("*");
    			}
    		}
    	}
    }

    Okay that just clicked what you meant, played around with my code some more
    and I have come up with this output which is correct except a space is placed here. I'm not sure if this will matter or not could you explain why it is there

    < there is a space here
    *
    **
    ***
    ****
    *****

  14. #14
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    Default Re: How do I do this, code supplied

    Quote Originally Posted by MooseManX View Post
    could you explain why it is there

    < there is a space here
    *
    **
    ***
    ****
    *****
    System.out.println();
    is the first thing inside the loop, so it is the first thing that happens
    Put the System.out.println(); somewhere else.
    If you worked this out on paper, step by step, it would have been clear how to make it work before you wrote public class ArgsLoop

  15. #15
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    Default Re: How do I do this, code supplied

    It's there, because the first thing you do in your outer loop is printing a new line. I bet when you used the pencil, the first thing was drawing a *, not moving to a new line

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    Default Re: How do I do this, code supplied

    public class ArgsLoop {
    	public static void main(String[] args) {
    	int n = Integer.parseInt(args[0]); // now n=5
    		for(int i=0;i<n;i++){
    			System.out.print("*");
    			System.out.println();
    			for(int c=i; c>-1; c--){
    				System.out.print("*");
    			}
    		}
    	}
    }
    If I separate them like this my output just becomes.

    *
    **
    ***
    ****
    *****
    *****
    again

  17. #17
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    Default Re: How do I do this, code supplied

    Back to the drawing board. (or pencil and paper)
    Hint, you do not need two lines that say System.out.print("*");
    Come up with how to do it first, then translate that solution to code

  18. #18
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    Default Re: How do I do this, code supplied

    public class ArgsLoop {
    	public static void main(String[] args) {
    	int n = Integer.parseInt(args[0]); // now n=5
    		for(int i=0;i<n;i++){
    			System.out.println();
    			for(int c=i; c>-1; c--){
    				System.out.print("*");
    			}
    		}
    	}
    }

    So I realized I do not need the outer * print. However this is still leaving me with a new line before the result

  19. #19
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    Default Re: How do I do this, code supplied

    When you did it on paper, (because we know you did this first, because it makes writing the code easier), did you move to a new line and then write *; or did you write * and then move to a new line?
    What does the code do? Write * or go to a new line first?

  20. #20
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    Default Re: How do I do this, code supplied

    For each row
    print c stars
    move to a new line

    Not that hard really.
    Improving the world one idiot at a time!

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