"while" loop not iterating correctly

Question

I am supposed to print the following output by using loops:

            1 
          2 1 
        3 2 1 
      4 3 2 1 
    5 4 3 2 1 
  6 5 4 3 2 1 
7 6 5 4 3 2 1

The highest number in this pattern (in this example, 7) is determined by user input. Here is the applicable code for the pattern:

index=patternLength+1; n=1;     //These values are all previously intitialized
while (index!=1) {
    index--;
    printSpaces((index*2)-2);   //A static method that prints a certain number of spaces
    while(n!=1) {
        n--;
        System.out.print(n + " ");
    }
    System.out.print("\n");
    n=patternLength+1-index;
}

And here is the incorrect output for the user input "7":

There are two blank lines preceding the incorrect output; these lines have the correct number of spaces necessary for the complete/correct pattern, but for some reason, the actual numbers start printing too "late" in the loop. In other words, the spaces that appear before the "1, 2 1" in the correct example are in the incorrect output. It's some of the numbers that are missing and make the incorrect example incorrect.

On the first iteration, n=1 so while(n!=1) skips immediately and no numbers are printed on the first row. --- At the end of the first iteration, index = patternLength+1 - 1 = patternLength, so n=patternLength+1-index = patternLength+1-patternLength = 1, so on the second iteration it will again skip the while(n!=1) loop and not print any numbers. --- Which part of that is confusing you, and why couldn't you see that for yourself with a debugger? — Andreas
– Andreas, Commented Feb 25, 2019 at 3:00
A. This is the "best" that I could do; when I try tweaking the loop controls, I get even stranger outputs (I can get examples if you'd like). B. I've not yet learned to use a debugger @Andreas — Brandon_J
– Brandon_J, Commented Feb 25, 2019 at 3:03
Perhaps I should change the title to "not iterating the way I want it to". — Brandon_J
– Brandon_J, Commented Feb 25, 2019 at 3:09
Ask yourself what the value of n is supposed to be. What does the value mean? Is it the count of numbers to print on the current row? If yes, the initial value of 1 is good, but loop condition while(n!=1) is bad, since you want it to iterate once for a value of 1. --- And you should then re-check the formula for calculating n for the second iteration, because you'd want n to be 2 on the second iteration. — Andreas
– Andreas, Commented Feb 25, 2019 at 3:15

Brandon_J · Accepted Answer · 2019-02-25 03:31:30Z

1

OK, I got it.

    index=patternLength+1; n=1;int nSetter=1;
    //Loop C
    System.out.println("Pattern C:");
    while (index!=1) {
        index--;
        printSpaces((index*2)-2);
        while(n!=0) {

            System.out.print(n + " ");
            n--;
        }
        System.out.print("\n");
        nSetter++;
        n = nSetter;
    }

My problem was that my "n" needed to go both up and down, so the extra variable "nSetter" seems to have solved that, although this may be a round-about solution. Whatever. Thanks to @Andreas for pointing me in the correct direction and @JohnKugelman for the helpful edit.

answered Feb 25, 2019 at 3:31

Brandon_J

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3 Comments

Alex Yu Over a year ago

I suggest you accept your own solution - it's an encouraged practice

Brandon_J Over a year ago

@AlexYu thanks, I just tried and it says that I have to wait two days. I'll accept it if I don't forget.

Alex Yu Over a year ago

Ah, OK. It's easy to not forget: you can always inspect your questions and answers on your profile page

Madhuka Dilhan · Accepted Answer · 2019-02-25 03:46:47Z

1

Please try this code your second while loop is not correct.

int index = patternLength + 1;
        int n = 2;     //These values are all previously intitialized
        int i = 1;
        while (index != 1) {
            index--;
            printSpaces((index * 2) - 2);   //A static method that prints a certain number of spaces
            while (n != 1) {
                n--;
                System.out.print(n + " ");
            }
            System.out.print("\n");
            i++;
            n = i+1;
        }

answered Feb 25, 2019 at 3:46

Madhuka Dilhan

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1 Comment

Brandon_J Over a year ago

Hmm...my code appears to work fine. Could you elaborate? Thanks for the answer!

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