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So I've been on this reflection in pset4's memory problem for well over an hour and I can't seem to get the first column of height to reflect. Only the first column too, everything else reflects.

here's what I have so far

//this determines where to stop reflecting; shows the midpoint for both even and odd numbers
    float mid = width / 2;
    if (width % 2 == 1)
    {
        mid = round(width);
    }
    
    //From each pixel, starting from images[0][0], it will swap its RGB with the pixel on the opposite side of the row. 
    for (int a = 0; a < height; a++)
    {
        for (int b = 0; b < (int) mid; b++)
        {
            
            int temp = image[a][b].rgbtRed;
            image[a][b].rgbtRed = image[a][width - b].rgbtRed;
            image[a][width - b].rgbtRed = temp;
            
            temp = image[a][b].rgbtBlue;
            image[a][b].rgbtBlue = image[a][width - b].rgbtBlue;
            image[a][width - b].rgbtBlue = temp;
            
            temp = image[a][b].rgbtGreen;
            image[a][b].rgbtGreen = image[a][width - b].rgbtGreen;
            image[a][width - b].rgbtGreen = temp;
            
        }
    }
    return;
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Think carefully about the values being used. Let's start with the first pixel, at 0,0, and that the image is 3x3 pixels.

image[a][b].rgbtRed = image[a][width - b].rgbtRed;

Fill in the numbers for the first pixel being processed in the first pass of the loop.

image[0][0].rgbtRed = image[0][3 - 0].rgbtRed;

This becomes:

image[0][0].rgbtRed = image[0][3].rgbtRed;

Now, what's the y value for the rightmost pixel? Is it 3 or 2?

BTW, there's some code that you can remove. First, what happens when you do integer division? Is there a fractional part in the result? Second, think through how the mid point works in a 3 wide line vs 4 wide line of pixels. Do you really need to do anything more than divide width by 2? ;-)

If this answers your question, please click on the check mark to accept. Let's keep up on forum maintenance. ;-)

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  • BTW, think about whether mid should be an int or a float. What happens to the test condition if mid, as a float, is just a hair smaller than the int value it is supposed to represent? (ie, 2.99999999997 vs. 3)
    – Cliff B
    May 28 at 5:00

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