how to print christmas tree for n in java

Question

public class tree {

 public static void main(String[] args) {
    int n ;
    Scanner input = new Scanner(System.in);
    System.out.println("Input value n:");
    n = input.nextInt();
    for (int i = 0; i < n; i=i+2) {
        for (int j = n/2; j==0; j--)
            System.out.print(" ");
        for (int k = 0; k <=i ; k++) 
            System.out.print("#");
             System.out.println();
    }
}

This is what requires in task:

What do i need to repair? And how to Print perform in function that is called from the main program?

@Milan Please have a look at this question as well, I believe that is exactly what you want http://stackoverflow.com/questions/43668323/programmatically-center-text-output-in-for-loop/43669102#43669102 — Yahya, May 20 '17 at 23:35
For starters, you need to replace `"*"` with `"#"`. Then you need to fix the `j` loop, because it always prints the same number of spaces. Don't you think the value of `i` would be needed to determine the number of spaces to print? — Andreas, May 21 '17 at 00:18
Sorry, first time using stackoverflow, the number n represents number of # in last row . — Milan Milosevic, May 21 '17 at 11:21

Andreas · Accepted Answer · 2017-05-21T01:16:08.283

Note that your code prints * characters, but should print # characters, and that there should be single spaces between the # characters.

 Wrong            Correct
   *                 #
  ***              # # #
 *****           # # # # #
*******        # # # # # # #

So, for the fun of it, here is an non-traditional way to do it the correct way for any size tree:

private static void printChristmasTree(int n) {
    final int w = n * 2 - 1;
    char[] buf = new char[w * 3 - 2];
    Arrays.fill(buf, ' ');
    for (int i = w - 1; i < buf.length; i += 2)
        buf[i] = '#';
    for (int s = 0; s < w; s += 2)
        System.out.println(new String(buf, s, s + w));
}

Output from printChristmasTree(6):

          #
        # # #
      # # # # #
    # # # # # # #
  # # # # # # # # #
# # # # # # # # # # #

Anyway, back to your code. Your output for n = 6 is:

*
***
*****

Your outer for loop uses i=i+2¹, which means you only get half the number of rows you need. Either change to i++, or change condition to i < n * 2. Let's go with second option, even though that would only make sense if you intended to print spaces between stars.
_{1) Better written as i += 2}

That changes output to:

*
***
*****
*******
*********
***********

Now the number of rows is correct, and the number of stars on each row is correct. Let's look at your space indenting loop.

Since j = n/2 = 3, the condition j==0 is immediately false, and that is why you don't get any spaces.

Perhaps you meant j != 0, but the problem is that the loop doesn't use the i value, so that would always print 3 spaces. We can fix that by starting the loop with j = n - i / 2 - 1.

Fixed code:

private static void printChristmasTree(int n) {
    for (int i = 0; i < n * 2; i += 2) {
        for (int j = n - i / 2 - 1; j > 0; j--)
            System.out.print(" ");
        for (int k = 0; k <= i; k++) 
            System.out.print("*");
        System.out.println();
    }
}

Output:

     *
    ***
   *****
  *******
 *********
***********

If we had chosen the first option earlier, i.e. change to i++, the code would be (with some other slight changes):

private static void printChristmasTree(int n) {
    for (int i = 0; i < n; i++) {
        for (int j = n - 1; j > i; j--)
            System.out.print(' ');
        for (int j = i * 2; j >= 0; j--) 
            System.out.print('*');
        System.out.println();
    }
}

Number of rows must be limited to when *=n , so if n=11 the result will be: * *** ***** ******* ********* *********** — Milan Milosevic, May 21 '17 at 07:11
@MilanMilosevic So `n` is the *width*, not the *height* (number of rows)? Perhaps that should have been clarified in the question. It also makes it more error-prone, i.e. what does `n = 6` mean? Having `n` be the height makes a lot more sense, but that never stopped a bad assignment. — Andreas, May 21 '17 at 08:49

how to print christmas tree for n in java

1 Answers1