How to create a Blur effect in C - c

Question

Part of a problem set for a course im doing (CS50) requires us to do apply a blur filter on an image. From a two dimensional array[i][j] we need to find the adjacent pixels to the one we want to blur and take the average RGB values and exchange them for the values in the pixel.
This is the code that I came up with yet it does not work.
I have watched some tutorials and they say to find the relative position of the pixel but i cannot really get my head aroud it.
Can anyone help me?
Here is the code I wrote for now:
// Blur image
void blur(int height, int width, RGBTRIPLE image[height][width])
{
int red = 0;
int green = 0;
int blue = 0;
int counter_pixel = 0;
//I would assume that we would need to tell the computer to free up space for the new imafe with malloc()
RGBTRIPLE temporary[height][width];
for (int i = 0; i < height; i++)
{
// go through every column
for (int j = 0; j < width; j++)
{
temporary[i][j] = image[i][j];
}
}
// go through every row
for (int i = 0; i < height; i++)
{
// go through every column
for (int j = 0; j < width; j++)
{
//checking if the pixel is inside the image
red = green = blue = 0;
if (i < 0 || j < 0 || i > height +1 || j > width + 1)
{
image[i + 1][j].rgbtRed = temporary[i + 1][j].rgbtRed;
image[i - 1][j].rgbtRed = temporary[i - 1][j].rgbtRed;
image[i][j + 1].rgbtRed = temporary[i][j + 1].rgbtRed;
image[i][j - 1].rgbtRed = temporary[i][j - 1].rgbtRed;
image[i + 1][j].rgbtGreen = temporary[i + 1][j].rgbtGreen;
image[i - 1][j].rgbtGreen = temporary[i - 1][j].rgbtGreen;
image[i][j + 1].rgbtGreen = temporary[i][j + 1].rgbtGreen;
image[i][j - 1].rgbtGreen = temporary[i][j - 1].rgbtGreen;
image[i + 1][j].rgbtBlue = temporary[i + 1][j].rgbtBlue;
image[i - 1][j].rgbtBlue = temporary[i - 1][j].rgbtBlue;
image[i][j + 1].rgbtBlue = temporary[i][j + 1].rgbtBlue;
image[i][j - 1].rgbtBlue = temporary[i][j - 1].rgbtBlue;
counter_pixel++;
red = round(((temporary[i + 1][j].rgbtRed + temporary[i - 1][j].rgbtRed + temporary[i][j + 1].rgbtRed + temporary[i][j -1].rgbtRed) / counter_pixel));
green = round(((temporary[i + 1][j].rgbtGreen + temporary[i - 1][j].rgbtGreen + temporary[i][j + 1].rgbtGreen + temporary[i][j -1].rgbtGreen) / counter_pixel));
blue = round(((temporary[i + 1][j].rgbtBlue + temporary[i - 1][j].rgbtBlue + temporary[i][j + 1].rgbtBlue + temporary[i][j -1].rgbtBlue) / counter_pixel));
}
}
}
return;
}