Codehs Fixed [updated] — 916 Checkerboard V1
A checkerboard pattern relies on the coordinates of the grid. For any cell located at row i and column j : Add the row index and the column index together ( i + j ). If the sum is , the cell gets a 0 . If the sum is odd , the cell gets a 1 .
In the landscape of introductory computer science, few tools are as effective for teaching logic as the CodeHS graphics library. Among the classic exercises presented to students is the creation of a checkerboard—a seemingly simple visual pattern that actually requires a deep understanding of coordinate systems, iteration, and conditional logic. The "916 Checkerboard v1" assignment is a specific variation of this problem that often trips up beginners. A "fixed" version of this code does more than just produce a pretty picture; it demonstrates the fundamental shift from linear thinking to algorithmic problem-solving.
If the board starts with black instead of red, simply swap the colors in the if-else block.
It sounds like you're referring to the and specifically the v1 version where you need to draw or create a checkerboard pattern, but there’s a common error you’re trying to fix.
: The program alternates between placing a "Ball-first" row and a "Blank-first" row. 916 checkerboard v1 codehs fixed
In the CodeHS 9.1.6 exercise, "Checkerboard v1," students must create an
// DO NOT USE THIS LOGIC int current = 0; for (int row = 0; row < grid.length; row++) for (int col = 0; col < grid[row].length; col++) grid[row][col] = current; current = (current == 0) ? 1 : 0; // Toggling the value Use code with caution. Why It Fails
int[][] board = new int[8][8]; declares an empty 2D integer array with 8 rows and 8 columns.
Here are some tips and tricks to help you solve the 916 Checkerboard V1 problem: A checkerboard pattern relies on the coordinates of the grid
If you would like to debug a specific error message you are receiving, please share the or the canvas dimensions required by your teacher. Share public link
The code can be broken down into a few logical steps:
The color must switch based on both the row and column index to create the staggered effect. The Logic Behind the Fix
This code creates a sharp, red-and-black checkerboard where the top-left square is black. If the sum is odd , the cell gets a 1
Because the sum of indices alternates perfectly across both dimensions, using the modulus operator ( % ) guarantees that your values will checkerboard seamlessly regardless of whether your grid dimensions are even or odd. Best Practices for CodeHS 2D Arrays
function moveToNextRow() if(facingEast()) turnLeft(); move(); turnLeft(); else turnRight(); move(); turnRight();
Always insert your row-ending actions (like a line break or moving a turtle graphics pointer down) outside the inner column loop, but inside the outer row loop. Alternative Karel / JavaScript Implementation Note
# Check if we are in the top 3 or bottom 3 rows (indices 0,1,2 and 5,6,7) if row < 3 or row > 4: # Loop through each of the 8 columns for col in range(8): # The (row + col) % 2 condition creates the checkerboard pattern if (row + col) % 2 == 0: current_row.append(1) else: current_row.append(0) else: # Fill the middle rows (indices 3 and 4) with 8 zeros for col in range(8): current_row.append(0)
Forgetting to "flip" the color starting point for every other row. The Fixed Code (JavaScript/Karel)
The most straightforward approach uses , a conditional operator ( if-else ) , and the % modulo operator to determine the pattern's alternation. This structure handles the entire board in one efficient process.