Need help making a blur effect in c

[odachi]

I had an assignment to make a blur effect in c. I'm using a 3x3 pixel sum avarage for the blur effect. It still doesnt work right and I dont understand what im doing right. It's supposed to be running correctly. Any help would be appreciated.

// Blur image
void blur(int height, int width, RGBTRIPLE image[height][width])
{
    RGBTRIPLE sum;
    int change;
    for(int i = 0; i < height; i++)
    {
        for(int j = 0; j < width; j++)
        {
            change = 0;
            sum.rgbtRed = 0;
            sum.rgbtGreen = 0;
            sum.rgbtBlue = 0;
            for(int y = -1; y < 2; y++)
            {
                //check if the row exists
                if(y + i > -1 && y + i < height)
                {
                for(int x = -1; x < 2; x++)
                {
                    //check if the pixel exists
                    if(x + j > -1 && x + j < width)
                    {
                        sum.rgbtRed += image[i + y][j + x].rgbtRed;
                        sum.rgbtGreen += image[i + y][j + x].rgbtGreen;
                        sum.rgbtBlue += image[i + y][j + x].rgbtBlue;
                        change++;
                    }
                }
                }
            }
            //if change is 0 then no pixels were found
            if(change != 0)
                //devide the sum by number of pixels found
                sum.rgbtRed = sum.rgbtRed / change;
                sum.rgbtGreen = sum.rgbtGreen / change;
                sum.rgbtBlue = sum.rgbtBlue / change;
                image[i][j] = sum;
        }
    }
    return;
}