AP CSA 2.11 Exercise 1: Rows and Columns

Unit 2: Selection and Iteration · Lesson 2.11 · Exercise 1

Rows and Columns

Nested Iteration. Write real Java, run it, and submit it to be graded against hidden test cases.

Back to the Lesson 2.11 page All Unit 2 lessons

Why this one is worth doing

The inner loop finishes completely for every single pass of the outer one. Printing a shape makes that visible, because a misplaced newline turns a rectangle into a column.

What to write

Read two integers, rows and cols.
Print a rectangle of asterisks with that many rows and columns, one row per line.
Print a left aligned triangle where row i has i asterisks, for i from 1 to rows.
Print the number of times the inner loop body ran while drawing the rectangle.
Print the number of times it ran while drawing the triangle.

Your program reads

Two integers on separate lines: rows, then cols. Both are at least 1.

Your program prints

The rectangle, then the triangle, then two counts.

Worked examples

These are the cases you can see. There are more you cannot, and they use different values, so an answer that prints these numbers as constants will fail.

Example 1 input

3
4

Example 1 output

****
****
****
*
**
***
12
6

Example 2 input

1
1

Example 2 output

*
*
1
1

Your answer

Main.java

import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    int rows = input.nextInt();
    int cols = input.nextInt();

    // System.out.print adds nothing after it. System.out.println ends the line.
  }
}

Input for the Run button

Run sends whatever is in the input box below. Submitting runs your program against every test case, including hidden ones with different input.

Stuck?

Hint 1

Use System.out.print inside the inner loop and an empty System.out.println() after it, so the line break happens once per row.

Hint 2

The triangle inner loop stops at the OUTER counter, not at cols. That single change is what makes it a triangle.

Hint 3

The rectangle count is always rows times cols. The triangle count is the sum 1 + 2 + ... + rows, which is why it grows more slowly.

Where to go next

Rework the Lesson 2.11 page Pick another Unit 2 lesson

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