(column * 50, row * 50) with size 50x50Row 0: R B R B R B R B
Row 1: B R B R B R B R
Row 2: R B R B R B R B
... and so on.
You are tasked with creating a checkerboard pattern using a grid of squares. The board should have 8 rows and 8 columns of alternating black and red squares. The top-left square should be red.
This is "v1" of the problem, meaning it likely expects a straightforward approach using nested loops and conditionals, without more advanced optimizations.
Create a 8x8 checkerboard using a loop. The checkerboard should have alternating black and white squares.
Inside the inner loop, we must move the turtle to the location of the next square.
If your code still doesn’t work after checking the logic above:
If you post your current non-working code (without asking for the full solution), I can point out the exact mistake.
In the CodeHS 9.1.6 exercise, "Checkerboard v1," students must create an
grid using a 2D list and populate it with a specific pattern of 0s and 1s. The final result must be an
grid where the top three and bottom three rows are filled with 1s, and the middle two rows are filled with 0s. 1. Core Concept and Requirements
The objective is to practice manipulating 2D lists (lists of lists) by accessing specific indices and using assignment statements. The autograder typically requires: Initialization: Creating an grid starting with all 0s.
Nested Loops: Iterating through the grid to modify specific elements.
Assignment: Explicitly setting grid[i][j] = 1 for the required rows rather than just printing the final output. 2. Common Errors in Initial Attempts
Many users encounter a "red" error in the autograder stating: "You should set some elements of your board to 1; You will need to use an assignment statement.". This occurs because:
Formatting over Logic: Users might print a checkerboard pattern using a string or a simple print loop without actually updating the 2D list structure.
Function Scope: Defining the print_board function inside another function, making it inaccessible. 916 checkerboard v1 codehs fixed
Incorrect Indexing: Failing to target exactly the top three (indices 0, 1, 2) and bottom three rows (indices 5, 6, 7). 3. The Fixed Solution Strategy
To fix the code and pass all CodeHS test cases, follow these structured steps: I. Initialize the 8x8 Grid
Create a 2D list containing eight sub-lists, each with eight zeros. grid = [] for i in range(8): grid.append([0] * 8) Use code with caution. Copied to clipboard II. Use Nested Loops for Assignment Iterate through every row ( ) and column (
). Use an if statement to check if the current row index is in the top three (less than 3) or bottom three (greater than 4). If it is, use an assignment statement to change the 0 to a 1.
for i in range(8): for j in range(8): if i < 3 or i > 4: grid[i][j] = 1 Use code with caution. Copied to clipboard III. Call the Print Function
Finally, pass your completed grid to the provided print_board function to display the result. Final Output Structure
The resulting 2D list represents a board where rows 0, 1, 2 and 5, 6, 7 are completely filled with 1s, creating the "v1" pattern required for the exercise.
Cracking the Grid: 916 Checkerboard v1 CodeHS Fixed If you’re working through the CodeHS JavaScript curriculum, Exercise 9.1.6: Checkerboard v1 is often the first major "wall" students hit. It requires you to move beyond simple loops and start thinking about 2D space, coordinates, and conditional logic.
If your circles are overlapping, only appearing on one line, or refusing to alternate colors, you’re in the right place. Here is the logic, the common bugs, and the fixed code to get your checkerboard working perfectly. The Logic Behind the Grid
To build a checkerboard, you have to tell the computer to do two things simultaneously: Create a Row: Place circles from left to right.
Create a Column: Repeat that row-making process from top to bottom.
This is achieved using Nested For Loops. The outer loop handles the vertical movement (y-coordinates), and the inner loop handles the horizontal movement (x-coordinates). Common Mistakes (Why your code is broken)
Before looking at the fix, check if you fell into these common traps:
Variable Scope: Using the same variable (like i) for both loops. This causes the loops to crash into each other.
Math Errors: Forgetting that radius is half of the diameter. If your circles are 40 pixels wide, you need to move 40 pixels to reach the next center point. Draw square at (column * 50, row * 50) with size 50x50
Color Logic: Forgetting to "flip" the color starting point for every other row. The Fixed Code (JavaScript/Karel)
Here is the clean, fixed solution for the 9.1.6 Checkerboard v1. This version uses constants to make it easy to adjust the size. javascript
/* This program draws a checkerboard pattern using nested loops. */ var RADIUS = 20; var DIAMETER = RADIUS * 2; function start() // Outer loop for the vertical rows (Y-axis) for (var row = 0; row < getHeight() / DIAMETER; row++) // Inner loop for the horizontal circles (X-axis) for (var col = 0; col < getWidth() / DIAMETER; col++) var x = col * DIAMETER + RADIUS; var y = row * DIAMETER + RADIUS; // Logic to determine color based on grid position if ((row + col) % 2 == 0) drawCircle(x, y, Color.red); else drawCircle(x, y, Color.black); function drawCircle(x, y, color) var circle = new Circle(RADIUS); circle.setPosition(x, y); circle.setColor(color); add(circle); Use code with caution. Breakdown of the Fix
row + col % 2: This is the "magic" math. By adding the row index and column index together and checking if the sum is even or odd, you create a perfect alternating pattern. Without this, every row would look identical.
col * DIAMETER + RADIUS: We multiply the column index by the diameter to move to the next "slot." We add the radius because circles in CodeHS are positioned by their center, not their top-left corner.
Dynamic Bounds: Using getWidth() / DIAMETER ensures that your checkerboard fills the screen regardless of how big the canvas is. Pro-Tip for CodeHS Debugging
If your circles aren't showing up, use console.log("Row: " + row + " Col: " + col); inside your inner loop. If you see the numbers printing in the console, your loops are working, and the issue is likely your circle.setPosition math! How are you planning to customize your checkerboard—
For the CodeHS assignment 9.1.6 Checkerboard, v1 , the goal is to create an
grid where the top three rows and bottom three rows are filled with s, while the middle two rows remain as Core Objective The exercise specifically tests your ability to access 2D lists assign new values using indexing. Common Mistakes & Fixes "You should set some elements to 1" Error
: This often happens if you create the grid rows already containing board.append([1]*8) ). CodeHS usually requires you to initialize a grid of all s first, then use a nested for loop assignment statement grid[r][c] = 1 ) to change specific values. Nested Loop Error : Ensure your print_board
function is defined outside your main loop to avoid scope issues. Incorrect Indexing : The middle rows (index 3 and 4) must remain . Your loop conditions should only target rows Step-by-Step Implementation Initialize the Grid list of lists filled entirely with ): my_grid.append([ Use code with caution. Copied to clipboard Use Nested Loops to Assign Values
Iterate through every row and column. Check if the row index is part of the top three ( is less than 3 ) or bottom three ( is greater than 4 : my_grid[r][c] = Use code with caution. Copied to clipboard Display the Result Pass your completed into the provided print_board print_board(my_grid) Use code with caution. Copied to clipboard Restated Solution
To fix the common autograder "assignment" error, you must first create a grid of zeros and then use nested loops to change the top and bottom three rows to grid[row][col] = 1 Need help with Checkerboard v2 or applying the modulus operator for alternating patterns?
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. Row 0: R B R B R B
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
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?
We use two loops:
The 916 Checkerboard problem on CodeHS is a classic challenge that requires creating a checkerboard pattern using a loop. Here is a fixed and well-documented solution: