Question

Doing some homework in my CSC 2310 class and I can’t figure out this one problem… it reads:

Write a program that will draw a right triangle of 100 lines in the
following shape: The first line, print 100 ‘‘, the second line, 99
‘’… the last line, only one ‘*’. Name the program as
PrintTriangle.java.

My code is pretty much blank because I need to figure out how to make the code see that when i = 100 to print out one hundred asterisks, when i = 99 print ninety-nine, etc. etc. But this is all i have so far:

public class PrintTriangle {
    public static void main(String[] args) {
        // Print a right triangle made up of *
        // starting at 100 and ending with 1
        int i = 100;
        while (i > 0) {
        // code here that reads i's value and prints out an equal value of *
            i--;
        }
    }
}

The rest of the assignment was way more difficult than this one which confuses me that I can’t figure this out. Any help would be greatly appreciated.

Answer 1

You clearly need 100 lines as you know. So you need an outer loop that undertakes 100 iterations (as you have). In the body of this loop, you must print i * characters on a single line, so you just need:

for (int j = 0 ; j < i ; j++) System.out.print("*");
System.out.println();  // newline at the end

Hence you will have:

int i = 100;
while (i > 0) {
    for (int j = 0; j < i; j++)
        System.out.print("*");
    System.out.println();
    i--;
}

Or equivalently,

for (int i = 100 ; i > 0 ; i--) {
    for (int j = 0; j < i; j++)
        System.out.print("*");
    System.out.println();
}

---

EDIT Using only while loops:

int i = 100;  // this is our outer loop control variable
while (i > 0) {
    int j = 0;  // this is our inner loop control variable
    while (j < i) {
        System.out.print("*");
        j++;
    }
    System.out.println();
    i--;
}

---

So to break it down:

• We have an outer loop that loops from i = 100 downwards to i = 1.

• Inside this outer while loop, we have another loop that loops from
  0 to i - 1. So, on the first iteration, this would be from 0-99
  (100 total iterations), then from 0-98 (99 total iterations), then
  from 0-97 (98 total iterations) etc.

• Inside this inner loop, we print a * character. But we do this i
  times (because it’s a loop), so the first time we have 100 *s, then 99, then 98 etc. (as
  you can see from the point above).

• Hence, the triangle pattern emerges.