If using CodeHS JavaScript (graphics):
If your actual CodeHS prompt differs, tell me the exact statement and I will adapt this write-up.
CodeHS Exercise 9.1.6: Checkerboard, v1 , the primary goal is to create a 2D list (a "grid") representing a checkers board using 1s for pieces and 0s for empty squares. Exercise Objectives Grid Initialization
: Create an 8x8 grid (list of lists) representing a game board. Specific Pattern top 3 rows bottom 3 rows should contain 1s. middle 2 rows should contain only 0s. Output Requirement : Use a provided print_board function to display the grid in a human-readable format. Key Logical Steps Initialize the Board : Create an empty list, typically named Fill the Top Rows
: Use a loop to append three rows, each containing eight 1s. Fill the Middle Rows : Append two rows of eight 0s. Fill the Bottom Rows : Append another three rows of eight 1s. Function Call : Pass the completed list to the print_board Common Implementation Strategies Simple Append board.append([1] * 8)
within loops is the most straightforward method for version 1. Nested Loops
: Some variations or autograders may require initializing the board with 0s first and then using nested loops to selectively assign to specific indices (e.g., board[i][j] = 1 Autograder Requirements : To pass all tests on , ensure you are using assignment statements
if the prompt specifically requests them, as simply printing the pattern without storing it in a grid may cause errors. Typical Pitfalls Incorrect Function Placement : Defining the print_board function inside another block or incorrectly indenting it. Missing Middle Rows
: Forgetting that the middle two rows (index 3 and 4 in an 8-row grid) must remain empty (0s). Bypassing Assignment
: Attempting to print the pattern directly instead of modifying the elements within a list structure. specific Python code
for these requirements, or are you looking for the logic behind Checkerboard v2 9.1.6 checkerboard v1 codehs
To create the 9.1.6 Checkerboard v1 in CodeHS, you need to use nested for loops to place circles in a grid pattern. 🏁 Core Logic The goal is to create an grid of circles. The outer loop controls the rows (vertical movement). The inner loop controls the columns (horizontal movement). The spacing is determined by the radius of the circle. 💻 Solution Code javascript
/* This program draws a checkerboard pattern using circles. * The board is 8x8. */ function start() // Calculate the radius based on canvas width (400) and 8 columns // Width / 8 = 50 per cell. Radius is 25. var radius = getWidth() / 16; // Outer loop for rows for (var row = 0; row < 8; row++) // Inner loop for columns for (var col = 0; col < 8; col++) // Calculate x and y positions var x = radius + (col * radius * 2); var y = radius + (row * radius * 2); // Create the circle var circle = new Circle(radius); circle.setPosition(x, y); // Alternate colors: // If (row + col) is even, color it gray. // If (row + col) is odd, color it red. if ((row + col) % 2 == 0) circle.setColor(Color.gray); else circle.setColor(Color.red); add(circle); Use code with caution. Copied to clipboard 🛠️ Key Concepts to Remember
Circle Sizing: Since the CodeHS canvas is 400 pixels wide and you need 8 circles, each "cell" is 50 pixels wide. The radius must be 25.
Spacing Formula: The center of the first circle is at radius. Every subsequent circle is moved by 2 * radius (the diameter).
The Modulo Trick: (row + col) % 2 == 0 is the standard way to create a "checkered" pattern. It ensures that no two circles of the same color are next to each other vertically or horizontally. 💡 Troubleshooting Tips
Circles overlapping? Ensure your position math uses (col * radius * 2). If you just use radius, they will all stack on top of each other.
Off-canvas? Check that your loop runs exactly 8 times. If it goes to 10, the circles will disappear off the right side.
Wrong colors? Make sure you are using Color.red and Color.gray (or whatever specific colors your assignment instructions require).
The "9.1.6 Checkerboard v1" exercise in CodeHS is a classic challenge designed to test your mastery of nested loops and 2D arrays (or grids). Creating a checkerboard pattern requires a logical approach to alternating colors based on row and column indices.
Here is a comprehensive breakdown of the logic, the code, and how to understand the underlying math. The Logic: Why a Checkerboard? In a standard If using CodeHS JavaScript (graphics): If your actual
grid, a checkerboard pattern alternates colors. If you look at the coordinates of any square: Square (0,0) is Color A. Square (0,1) is Color B. Square (1,0) is Color B. Square (1,1) is Color A.
The mathematical secret to this pattern is the sum of the indices. If you add the row index and the column index Even sums result in one color. Odd sums result in the other color. The Code Implementation
Most CodeHS versions of this exercise use the Grid class or a simple graphics library. Below is the standard structural approach using nested for loops. javascript
function start() // Define the size of the board var NUM_ROWS = 8; var NUM_COLS = 8; // Outer loop handles the rows for (var row = 0; row < NUM_ROWS; row++) // Inner loop handles the columns for (var col = 0; col < NUM_COLS; col++) // Check if the sum of row and col is even if ((row + col) % 2 == 0) drawSquare(row, col, Color.red); else drawSquare(row, col, Color.black); function drawSquare(row, col, color) var sideLength = getWidth() / 8; var x = col * sideLength; var y = row * sideLength; var rect = new Rectangle(sideLength, sideLength); rect.setPosition(x, y); rect.setColor(color); add(rect); Use code with caution. Key Components Explained 1. Nested Loops
The outer loop (row) tells the program to start at the top and move down. For every single row, the inner loop (col) runs across from left to right. This ensures every single coordinate on the grid is visited. 2. The Modulo Operator (%) The line (row + col) % 2 == 0 is the "brain" of the code. % 2 finds the remainder when divided by 2. If the remainder is 0, the number is even.
This creates the perfect alternating "staircase" effect needed for the checkerboard. 3. Coordinate Scaling
In CodeHS, simply saying "Row 1" doesn't tell the computer where to draw on the screen. You must multiply the row or col by the sideLength of the square to get the actual pixel position Common Pitfalls
Off-by-one errors: Ensure your loops run from 0 to NUM_ROWS - 1. Using <= instead of < will often result in the board drawing off the screen.
Variable Confusion: Swapping row and col inside the setPosition function is the most common reason for a "sideways" or broken grid. Remember: X is Columns, Y is Rows.
By mastering this exercise, you aren't just drawing a grid; you are learning how data is structured in almost every modern software application—from Excel spreadsheets to the pixels on your monitor. If you want, tell me which language or
Are you having trouble with a specific error message in your CodeHS console, or does the logic of the modulo operator make sense now?
This exercise focuses on using nested loops modulus operator
) to create a grid pattern. In the 9.1.6 Checkerboard assignment, the goal is to alternate colors (usually black and red) across a grid of squares. Key Concepts Nested Loops : You use an outer loop for the and an inner loop for the
. This ensures that for every row created, the program draws a full set of squares across the screen. The Modulus Strategy
: To get the "checkerboard" effect, you can't just alternate colors every other square, because each new row needs to start with a different color than the one above it to prevent vertical stripes. The Formula : A common trick is to add the current row index ( ) and column index ( (i + j) % 2 == 0 , use Color A. Otherwise, use Color B. Implementation Tips SQUARE_SIZE
to keep your code flexible. If you change the size of one square, the whole board should adjust automatically. : Create a drawSquare(x, y, color)
function to keep your loops clean. Passing the coordinates and color as parameters makes the logic much easier to read. By mastering this, you’re learning how computers handle coordinate systems conditional rendering
, which are the building blocks of game design and UI development. code snippet
illustrating how to apply the modulus math within the loops?
var size = 8;
var S = 40; // pixel square size
for (var r = 0; r < size; r++)
for (var c = 0; c < size; c++)
var x = c * S;
var y = r * S;
if ((r + c) % 2 === 0)
fillRect(x, y, S, S); // filled square
else
// leave background or draw empty square
If you want, tell me which language or CodeHS API (console vs. graphics) you're using and I can produce a ready-to-run solution.
(Invoking related search terms)
This document analyzes the problem titled "9.1.6 checkerboard v1" from CodeHS (assumed exercise naming), reconstructs likely requirements, explains correct algorithmic approaches, provides a rigorous step‑by‑step solution, proves correctness, highlights edge cases, and offers an annotated reference implementation in Python (readable pseudocode for educators/students). Assumptions about the exact original prompt are made explicit where the source problem text is unavailable.