cs50 pset4 filter swapping structs - c

Question

I'm facing some difficulties while doing the reflect portion of filter. Essentially the struct is
typedef struct
{
BYTE rgbtBlue;
BYTE rgbtGreen;
BYTE rgbtRed;
} __attribute__((__packed__))
RGBTRIPLE;
and I have been attempting to reflect the image by implementing this function.
void reflect(int height, int width, RGBTRIPLE image[height][width])
{
for (int i = 0; i < height; i++)
{
if (width % 2 == 0)
{
for (int j = 0; j < width/2; j++)
{
RGBTRIPLE temp = image[i][j];
image[i][j] = image[i][width - j];
image[i][width - j] = temp;
}
}
else if (width % 3 == 0)
{
for (int j = 0; j < (width - 1)/2; j++)
{
RGBTRIPLE temp = image[i][j];
image[i][j] = image[i][width - j];
image[i][width - j] = temp;
}
}
}
return;
}
The code compiles fine but the end product is the same as the input image. Tried to run debug50 and i figured that my problem lies with the way i swap the RGBTRIPLE values. Any help would be good. Thanks!

Answer 1

What you need to do is to reverse the array.
Why? because you are reflecting image horizontally so you want the left side of the image to become the right side of the image.
Imagine you have this array and you want to reverse it:
int count = 5;
int numbers[count] = {0, 1, 2, 3, 4};
// middle here should be 2.5 but it will be 2 because we cast it to int
int middle = count / 2;
// Reverse array
for (int i = 0; i < middle; i++)
{
// when i is 0, numbers[i] is 0, numbers[count - 1 - i] is 4
temp = numbers[i];
numbers[i] = numbers[count - i - 1];
numbers[count - i - 1] = temp;
}
You should do the same in your function:
// Reflect image horizontally
void reflect(int height, int width, RGBTRIPLE image[height][width])
{
// The middle index
int middle = width / 2;
for (int i = 0; i < height; i++)
{
for (int j = 0; j < middle; j++)
{
// Swap the left side element with right side element
RGBTRIPLE temp = image[i][j];
image[i][j] = image[i][width - j - 1];
image[i][width - j - 1] = temp;
}
}
return;
}