Why does it not round up correctly?

Question

So i'm doing filter and I noticed that its not rounding up correctly.

// Convert image to grayscale
void grayscale(int height, int width, RGBTRIPLE image[height][width])
{
    // Iterate over height
    for (int h = 0; h < height; h++)
    {
        // Iterare over width
        for (int w = 0; w < width; w++)
        {
            // Calculate the average of rgbt
            int k = round((image[h][w].rgbtBlue + image[h][w].rgbtGreen + image[h][w].rgbtRed)/3);

            // Update rgbt
            image[h][w].rgbtBlue = k;
            image[h][w].rgbtGreen = k;
            image[h][w].rgbtRed = k;
        }
    }
    return;
}

:) helpers.c exists

:) filter compiles

:) grayscale correctly filters single pixel with whole number average

:( grayscale correctly filters single pixel without whole number average expected "28 28 28\n", not "27 27 27\n"

:) grayscale leaves alone pixels that are already gray

:) grayscale correctly filters simple 3x3 image

:( grayscale correctly filters more complex 3x3 image expected "20 20 20\n50 5...", not "20 20 20\n50 5..."

:( grayscale correctly filters 4x4 image expected "20 20 20\n50 5...", not "20 20 20\n50 5..."

So I tried to run the file to se what was happening and

$ ./filter -g yard.bmp test.bmp

Could not open yard.bmp.

Answer 1

You are dividing an integer by an integer. This is integer division, and will produce an integer again, ignoring the fractional part.

You could make it a floating point division by making at least one operand floating point, like replacing 3 with 3.0.