/**
   This class describes triangle objects that can be displayed
   as shapes like this:
   []
   [][]
   [][][]
*/
public class Triangle
{
   /**
      Constructs a triangle.
      @param aWidth the number of [] in the last row of the triangle.
   */
   public Triangle(int aWidth)
   {
      width = aWidth;
   }

   /**
      Computes a string representing the triangle.
      @return a string consisting of [] and newline characters
   */
   public String toString()
   {
      String r = "";
      for (int i = 1; i <= width; i++)
      {  
         // Make triangle row
         for (int j = 1; j <= i; j++)
            r = r + "[]";
         r = r + "\n";
      }
      return r;
   }

   private int width;
}

/**
   This program prints two triangles.
*/
public class TriangleRunner
{
   public static void main(String[] args)
   {
      Triangle small = new Triangle(3);
      System.out.println(small.toString());

      Triangle large = new Triangle(15);
      System.out.println(large.toString());
   }
}

How would you modify the nested loops so that you print a square instead of a triangle? 
   Answer: Change the inner loop to for (int j = 1; j <= width; j++) 

What is the value of n after the following nested loops?
int n = 0;
for (int i = 1; i <= 5; i++)
   for (int j = 0; j < i; j++)
      n = n + j;

   Answer: 20.