9.1.6 Checkerboard V1 Codehs Jun 2026

public class Checkerboard extends ConsoleProgram public static void main(String[] args) int size = 8; int[][] board = new int[size][size]; for (int row = 0; row < size; row++) for (int col = 0; col < size; col++) // Check if the sum of row and col is even if ((row + col) % 2 == 0) board[row][col] = 1; // "Color A" else board[row][col] = 0; // "Color B" // Helper method to print the board printBoard(board); private static void printBoard(int[][] board) for (int[] row : board) for (int val : row) System.out.print(val + " "); System.out.println(); Use code with caution. Copied to clipboard Visual Representation Key Concepts to Remember : int[][] board = new int[rows][cols];

rect.setColor(Color.BLACK);

CodeHS often checks for exact constant names and specific colors. If the autograder fails, verify if your assignment requires specific colors (like "white" instead of "red") or exact variable names specified in the prompt instructions. Are there specific colors your prompt asks you to use? Share public link 9.1.6 checkerboard v1 codehs

int[][] board = new int[8][8]; for (int row = 0; row < 8; row++) for (int col = 0; col < 8; col++) if ((row + col) % 2 == 0) board[row][col] = 0; else board[row][col] = 1; Use code with caution. Copied to clipboard Common Pitfalls

The for row in range(NUM_SQUARES): loop starts at row 0. Before moving to row 1, it triggers the inner for col in range(NUM_SQUARES): loop, which runs through columns 0 to 7. This ensures every single grid position is visited. Calculating Share public link int[][] board = new int[8][8];

Which specific (JavaScript or Python) your CodeHS course is using?

Hardcoding pixel values makes code fragile and unresponsive to screen resizing. This solution uses getWidth() to automatically adapt to any canvas size: If the remainder is 0

def draw_checkerboard(n, square_size, color1, color2): for r in range(n): for c in range(n): color = color1 if (r + c) % 2 == 0 else color2 draw_filled_square(x=c*square_size, y=r*square_size, size=square_size, fill=color)

# Mastering CodeHS 9.1.6 Checkerboard v1: A Complete Guide Building a checkerboard grid is a classic computer science problem. In the CodeHS JavaScript track, exercise **9.1.6 Checkerboard v1** challenges you to use nested loops and programming logic to draw a grid of alternating colored squares. This guide breaks down the concept, the logic, and the complete solution to help you understand how to write and optimize this code. ## Understanding the Goal The objective of Checkerboard v1 is to create an 8x8 grid of squares on the screen. The squares must alternate colors (usually black and red, or black and white) both horizontally and vertically, perfectly mimicking a real-life checkerboard. ### Key Technical Concepts * **Nested Loops:** Using a loop inside another loop to control rows and columns. * **Conditional Logic (If/Else):** Determining which color to paint a square based on its position. * **Coordinate Math:** Calculating the exact pixel coordinates $(x, y)$ for each square so they do not overlap. --- ## Breakdown of the Logic To build an 8x8 grid, you cannot just draw 64 squares manually. You need a system that loops through 8 rows, and inside each row, loops through 8 columns. ### 1. The Grid Math Assume the screen or grid width is divided equally. If each square is $40 \times 40$ pixels: * **Column 0** starts at $x = 0$ * **Column 1** starts at $x = 40$ * **Column 2** starts at $x = 80$ * Formula for X: `col * SQUARE_SIZE` * Formula for Y: `row * SQUARE_SIZE` ### 2. The Alternating Color Logic How do we know if a square should be Color A or Color B? We look at the grid coordinates `(row, col)`. If you add the current row index and column index together (`row + col`), a pattern emerges: * Row 0, Col 0 $\rightarrow 0 + 0 = 0$ (Even $\rightarrow$ Color A) * Row 0, Col 1 $\rightarrow 0 + 1 = 1$ (Odd $\rightarrow$ Color B) * Row 1, Col 0 $\rightarrow 1 + 0 = 1$ (Odd $\rightarrow$ Color B) * Row 1, Col 1 $\rightarrow 1 + 1 = 2$ (Even $\rightarrow$ Color A) By using the modulo operator (`% 2`), we check if `(row + col)` is divisible by 2. If the remainder is 0, it is an even position; otherwise, it is odd. --- ## CodeHS 9.1.6 Checkerboard v1 Code Solution Here is the complete JavaScript solution using the CodeHS graphics library. ```javascript // Constants for the checkerboard setup var NUM_ROWS = 8; var NUM_COLS = 8; var SQUARE_SIZE = 40; // Adjust based on your specific assignment window size function start() drawCheckerboard(); function drawCheckerboard() // Outer loop controls the rows (vertical movement) for (var row = 0; row < NUM_ROWS; row++) // Inner loop controls the columns (horizontal movement) for (var col = 0; col < NUM_COLS; col++) // Calculate coordinates for the current square var x = col * SQUARE_SIZE; var y = row * SQUARE_SIZE; // Create the square object var square = new Rectangle(SQUARE_SIZE, SQUARE_SIZE); square.setPosition(x, y); // Alternating color logic using row and column indices if ((row + col) % 2 === 0) square.setColor(Color.RED); else square.setColor(Color.BLACK); // Add the square to the screen add(square); ``` --- ## Detailed Code Step-by-Step Walkthrough ### Step 1: Defining Constants We define `NUM_ROWS`, `NUM_COLS`, and `SQUARE_SIZE` at the top. This makes the code adaptable. If you want to change it to a 10x10 board later, you only have to change the constants, not the core logic. ### Step 2: The Outer Loop (`row`) The outer loop runs 8 times. It starts at `row = 0` and stops when `row = 7`. This dictates the vertical $y$-axis progression. ### Step 3: The Inner Loop (`col`) For *every single iteration* of the outer loop, the inner loop runs 8 times. This draws 8 individual squares from left to right before moving down to the next row. ### Step 4: The `if/else` Condition The line `if ((row + col) % 2 === 0)` evaluates the mathematical rule we established earlier. * If true, it assigns `Color.RED`. * If false, it defaults to `Color.BLACK`. ### Step 5: Rendering `add(square)` places the fully configured rectangle object onto the canvas canvas at the calculated `(x, y)` coordinate. --- ## Common Mistakes to Avoid 1. **Mixing up X and Y coordinates:** Remember that columns move horizontally along the X-axis (`col * SQUARE_SIZE`), while rows move vertically down the Y-axis (`row * SQUARE_SIZE`). Swapping these will corrupt the grid rendering. 2. **Forgetting to update loop variables:** Ensure your loop conditions use `row++` and `col++` so you do not accidentally trigger an infinite loop that crashes the CodeHS browser tab. 3. **Using a single loop:** Trying to draw all 64 squares in a single loop using complex division math is messy. Always use nested loops for 2D grids. Use code with caution. If you want to customize this further, let me know:

Within those specific rows, use modular arithmetic—specifically (row + column) % 2 —to decide if a cell should be a