916 Checkerboard V1 Codehs Fixed Online
| Mistake | Why It Happens | Fix |
|---------|----------------|------|
| Colors are offset (e.g., top-left black) | Used (row + col) % 2 === 1 for red | Use === 0 for red |
| Board starts red but columns don't alternate | Forgot to add row and col together | Use (row + col) % 2 |
| Squares overlap or wrong spacing | Used same x/y for all squares | Multiply by squareSize |
| Board is only 4x4 or wrong size | Wrong number of rows/cols | Set numRows = 8, numCols = 8 |
The 916 Checkerboard V1 problem on CodeHS is a popular challenge that requires students to create a checkerboard pattern using code. Here is a fixed solution to the problem:
Problem Statement: Create a checkerboard with 8 rows and 8 columns, with alternating black and white squares.
Fixed Code:
# Initialize the canvas
canvas_width = 400
canvas_height = 400
create_canvas(canvas_width, canvas_height)
# Define the square size
square_size = 50
# Loop through rows and columns to draw the checkerboard
for row in range(8):
for col in range(8):
# Alternate between black and white squares
if (row + col) % 2 == 0:
fill_color = "white"
else:
fill_color = "black"
# Draw the square
fill(fill_color)
rect(col * square_size, row * square_size, square_size, square_size)
Explanation:
Tips and Variations:
Example Use Case: Run the code to see a fully functional checkerboard with alternating black and white squares.
Mastering the 916 Checkerboard v1: Solutions and Logic for CodeHS
If you are working through the CodeHS curriculum, you’ve likely encountered the 9.1.6 Checkerboard v1 assignment. It’s a classic challenge that tests your ability to use nested loops, coordinate systems, and conditional logic.
However, getting the "fixed" version—where the grid perfectly alternates colors without overlapping or skipping—can be tricky. The objective is to create an
grid of squares where the colors alternate between black and red (or other assigned colors), resembling a standard checkerboard. Key Technical Requirements:
Nested Loops: You need an outer loop for rows and an inner loop for columns.
Size Calculations: Each square must be the width of the canvas divided by 8.
The "Fixed" Logic: The color must switch based on both the row and column index to create the staggered effect. The Logic Behind the Fix
The most common mistake in "v1" is only checking if the column is even or odd. If you do that, every row will look identical, resulting in vertical stripes rather than a checkerboard. The Solution: Use the sum of the row and column indices. If (row + col) is even, color it Red. If (row + col) is odd, color it Black. The Corrected Code (JavaScript/Karel Style)
Here is a clean, "fixed" implementation for the CodeHS environment: javascript
var SQUARES_PER_SIDE = 8; var SQUARE_SIZE = getWidth() / SQUARES_PER_SIDE; function start() for (var row = 0; row < SQUARES_PER_SIDE; row++) for (var col = 0; col < SQUARES_PER_SIDE; col++) drawSquare(row, col); function drawSquare(row, col) var x = col * SQUARE_SIZE; var y = row * SQUARE_SIZE; var rect = new Rectangle(SQUARE_SIZE, SQUARE_SIZE); rect.setPosition(x, y); // The "Fixed" Logic: Check if sum of indices is even if ((row + col) % 2 == 0) rect.setColor(Color.red); else rect.setColor(Color.black); add(rect); Use code with caution. Troubleshooting Common Errors 1. The "Off-by-One" Pixel Gap 916 checkerboard v1 codehs fixed
If you see white lines between your squares, ensure you are calculating SQUARE_SIZE using getWidth() / 8. If you hardcode a number like 50 on a canvas that isn't exactly 400, the grid won't fit perfectly. 2. Rectangles Overlapping the Border
Make sure your setPosition uses col * SQUARE_SIZE for the X-coordinate and row * SQUARE_SIZE for the Y-coordinate. Swapping these can sometimes cause the grid to render incorrectly if your canvas isn't a perfect square. 3. Infinite Loops
Ensure your for loop conditions use < SQUARES_PER_SIDE and not <=. Using <= will attempt to draw a 9th row/column, which usually breaks the layout or triggers a "limit exceeded" error in CodeHS.
The "916 checkerboard v1 codehs fixed" solution relies entirely on the row + column parity. Once you master the nested loop structure, you can apply this logic to more complex grid-based games like Minesweeper or Chess.
Are you having trouble with the v2 version of this assignment, or is the autograder still giving you a specific error message?
The core objective of CodeHS 9.1.6: Checkerboard, v1 is to practice modifying 2D lists using nested loops and index-based assignment.
The autograder often fails students who simply print the pattern; it strictly requires that you initialize a board of 0s and then use assignment statements (e.g., board[i][j] = 1) to place pieces. Fixed Python Solution
This code initializes an 8x8 grid of zeros and then fills the top three and bottom three rows with a checkerboard pattern of 1s.
# Function to print the board def print_board(board): for row in board: # Join elements with a space for proper formatting print(" ".join([str(x) for x in row])) # 1. Initialize an 8x8 board with all zeros board = [] for i in range(8): board.append([0] * 8) # 2. Use nested loops to assign 1s to specific indices # Row indices 0, 1, 2 are the top three rows # Row indices 5, 6, 7 are the bottom three rows for row in range(8): for col in range(8): # Check if the row should have pieces if row < 3 or row > 4: # Only set to 1 if (row + col) is even to create the pattern if (row + col) % 2 == 0: board[row][col] = 1 # 3. Display the final board print_board(board) Use code with caution. Copied to clipboard Key Logic & Fixes 💡
Explicit Assignment: You must use board[row][col] = 1. The autograder specifically looks for the = assignment operator being used on the list elements.
The Modulo Trick: Using (row + col) % 2 == 0 ensures that the 1s alternate correctly across both rows and columns.
Row Filtering: The condition if row < 3 or row > 4 targets the "top 3" (0, 1, 2) and "bottom 3" (5, 6, 7) rows as required by the exercise.
String Formatting: Using " ".join(...) ensures the output matches the expected CodeHS console format exactly, preventing "Output does not match" errors. Common Errors to Avoid
Defining print_board inside another function: This leads to scope errors where the autograder can't find your display logic.
Using hardcoded print statements: Printing 1 0 1 0... directly will pass the visual check but fail the "You should set some elements of your board to 1" test.
If you're also working on 9.1.7: Checkerboard, v2, let me know—the logic changes slightly to focus on a full-board pattern or different row offsets. | Mistake | Why It Happens | Fix
To fix the 9.1.6 Checkerboard V1 exercise in CodeHS (Karel), the primary challenge is ensuring the "ball" pattern alternates correctly regardless of whether the row has an even or odd number of spaces.
The following structure resolves the common issue where Karel places two balls in a row or skips a corner when moving to the next level: Fixed Code Structure (Karel JavaScript) javascript
/* * This program draws a checkerboard pattern. * The "Fixed" version ensures that rows alternate * regardless of the grid dimensions. */
(leftIsClear() || frontIsClear()) fillRow(); resetToNextRow(); } // Fills a single row with alternating balls fillRow() putBall(); (frontIsClear()) move();
(frontIsClear()) move(); putBall();
// Handles the transition between rows and pattern alignment resetToNextRow() (facingEast())
(leftIsClear()) turnLeft(); move(); turnLeft();
(rightIsClear()) turnRight(); move(); turnRight(); } Use code with caution. Copied to clipboard Key Fixes Applied The "Double Move" Logic , checking frontIsClear() twice ensures Karel doesn't attempt to
into a wall or place a ball incorrectly at the end of a row. Alternating Logic
: If your specific version requires the second row to start with a gap, add a check in resetToNextRow
to see if a ball was placed in the last corner before moving up. Loop Termination uses an OR condition (
) to ensure Karel finishes the very last row even if there is no "left" to move into.
: Since CodeHS assignments vary slightly by version (Karel vs. Python), make sure your function names ( ) match your specific course requirements. Java Karel
The critical line that fixes most student errors is:
if ((row + col) % 2 == 0)
Before we jump to the "fixed" code, let’s break down the assignment’s requirements:
The most common "non-fixed" issues students encounter: The 916 Checkerboard V1 problem on CodeHS is
After implementing the code above, run the program. You should see:
If the board starts with black instead of red, simply swap the colors in the if-else block.
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.
The Illusion of Simplicity
At first glance, a checkerboard appears trivial. It is simply a grid of alternating red and black squares. A student’s first instinct is often to "hard code" the solution: draw a red square, then a black square, then a red square, and manually position them one by one. However, the "916" specification usually implies a large grid (likely 8x8 or similar dimensions), making hard-coding impractical and tedious. The "fixed" solution abandons the manual approach in favor of automation, using nested loops to traverse the rows and columns.
The beauty of the fixed code lies in its use of the for loop. By nesting a column loop inside a row loop, the program efficiently visits every coordinate on the grid. This structure teaches students how computers handle two-dimensional space: not as a continuous canvas, but as a matrix of discrete points defined by x and y coordinates.
The Logic of Alternation
The core challenge of the "916 Checkerboard" is not drawing the squares, but determining their color. This is where many early attempts fail. A common misconception is that the color alternates simply based on the loop counter (e.g., if i is even, red; if i is odd, black). While this works for a single line, it fails on a grid because the first square of a new row must be the opposite color of the last square of the previous row.
The "fixed" solution solves this through modular arithmetic. The logic typically follows a formula checking the sum of the row and column indices:
if ((row + col) % 2 == 0)
// Draw Red Square
else
// Draw Black Square
This is the "aha!" moment for the assignment. It teaches that patterns in computer science are often mathematical. By checking if the sum of the coordinates is even or odd, the code automatically creates the staggered pattern required for a checkerboard, regardless of the grid size.
Fixing Common Errors
Why is the "fixed" version necessary? The "v1" designation implies an iterative process. Common errors in the unfixed versions include:
The "fixed" code addresses these by ensuring the loop parameters match the grid dimensions precisely and that the offset logic (row + col) is implemented correctly.
Conclusion: Beyond the Graphics
The "916 Checkerboard v1 CodeHS Fixed" is not just a solution to a homework assignment; it is a milestone in a programmer's education. It transitions a student from a human who gives manual instructions to a programmer who designs algorithms. The fixed code is efficient, readable, and mathematically elegant. By mastering the logic required to fix this checkerboard, students gain the foundational skills necessary to tackle more complex problems, from rendering game boards to managing large data sets in two-dimensional arrays.
We use two loops: