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Thread: Upside down Triangle pattern
 06062011, 04:37 AM #1Member
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Upside down Triangle pattern
Hi Sorry if this is something that is often posted but I don't understand why the way I did it doesn't work and I'd like to find out why it doesn't.
The first triangle i did started as such
*
**
***...
This time I'd like to switch it upside down as follows
***
**
*
I did this by using the loop the opposite as I did with the first and instead of having j = 0 and incrementing it, i made j = n and decremented j.
Java Code:// loop N times, one for each row for (int i = n; i <= n; i) { // print j periods for (int j = i; j <= i; j) System.out.print("*"); // print a new line System.out.println(); }
Any help is greatly appreciated!
 06062011, 04:53 AM #2
Assume i = 1
You assign the value of i to j, j is 1.
Is j <= i? Is 1 less than or equal to 1? Yes.
Decrement j, j is now 0;
Is j <= i? Is 0 less than or equal to 1? Yes.
Decrement j, j is now 1;
Is j <= i? Is 1 less than or equal to 1? Yes.
etc
Questions about these star shape programs are always popping up on forums. My advice always is to write another method which takes 2 parameters: the character to be printed on a single line and the number of times it should be printed. Then back in your main method you have a loop that iterates "lines" number of times calling the print method. Now all you have to do is work out the algorithm for how many *'s (and possibly spaces) need to be printed on wach line.Last edited by Junky; 06062011 at 05:07 AM.
 06062011, 04:53 AM #3Member
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Deconstruct your inner for loop.
 06062011, 05:00 AM #4Member
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What do you mean deconstruct my inner loop?
 06062011, 05:02 AM #5Member
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 06062011, 05:10 AM #6Member
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Why is one of the i's ever be 1? if i = n, and j = i? I'm a little confused.
 06062011, 05:18 AM #7Member
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I also get an infinite loop when I change the parameter to j>=i.
 06062011, 05:24 AM #8Member
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Oh, I see, since j will always be bellow i. So is my entire methodology wrong by using decrements to trying to invert the triangle?
 06062011, 05:25 AM #9
It is because your logic is wrong and you are just guessing. That does not work when it comes to programming. Walk away from the computer, grab a pencil and some paper, write down how many stars appear on each line. Do this for 3 rows, 4 rows, 5 rows etc. Then see if a pattern emerges. Once you have done that you can write the code.
Also did you ignore my advice about writing a separate method? If you do write this method you should find writing the code much easier. Plus it can be used for all such programs.
 06062011, 05:46 AM #10Member
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