CodeHS 8.14.4：Summing Grid问题求助——JavaScript函数异常排查

The Problem #

You need a sumGrid(grid) function that fills each grid position with the sum of its row index and column index, then outputs the values in order. For a Grid(2, 3) (2 rows, 3 columns), the expected output is 0 1 2 1 2 3, but your current code outputs 0 1 2 1 2 undefined.

What's Wrong With Your Current Code #

Let's break down the issues in your sumGrid function:

• You’re modifying the outer loop’s row variable inside the inner loop (row += 1), which completely breaks the loop’s iteration logic.
• You’ve added two separate nested loops that don’t work together—you’re first printing row indices, then trying to print column indices, instead of calculating their sum directly.
• You’re re-declaring row inside the second loop, causing scope confusion, and your col initialization is incorrect, leading to the undefined value at the end.
• Most importantly: you never actually calculate the sum of the row and column indices anywhere in your code!

Fixed Code #

Here's the corrected version of the sumGrid function that meets your requirements:

function start(){ 
  var grid = new Grid(2, 3); 
  println(sumGrid(grid)); 
}

function sumGrid(grid){
  // Create an array to collect all sum values for clean formatting
  var result = [];
  // Loop through each row index
  for(var row = 0; row < grid.numRows(); row++){
    // Loop through each column index in the current row
    for(var col = 0; col < grid.numCols(); col++){
      // Calculate the sum of row and column index
      var cellSum = row + col;
      // Add the sum to our result array
      result.push(cellSum);
    }
  }
  // Convert the array to a space-separated string and return it
  return result.join(" ");
}

How This Works #

1. Result Collection: Using an array to store sums ensures we avoid extra trailing spaces or messy newlines in the final output.
2. Consistent Loops: The outer loop handles row indices, and the inner loop handles column indices—no modification of loop variables inside the loops, so iteration stays predictable.
3. Direct Sum Calculation: For every cell, we compute row + col exactly as the problem requires.
4. Clean Formatting: join(" ") converts the array into a neat space-separated string that matches the expected output.

Alternative: Direct Printing (If You Don't Need to Return the String) #

If you prefer to print directly instead of returning a formatted string, you can adjust the function like this:

function sumGrid(grid){
  var output = "";
  for(var row = 0; row < grid.numRows(); row++){
    for(var col = 0; col < grid.numCols(); col++){
      output += (row + col) + " ";
    }
  }
  // Trim the trailing space before printing
  println(output.trim());
}

This will print the exact expected output: 0 1 2 1 2 3

内容的提问来源于stack exchange，提问作者Sophia Simpson