Why does it say that my index it -1?

Question

I am working on blur in filter and it says my index is our if bound -1

        // Create count starts and end count
        int sh = -1;
        int eh = 1;
        int sw = -1;
        int ew = 1;

        //Modify start for first height
        if (h == 0)
        {
            sh = 0;
        }
        if (h == height - 1)
        {
            eh = 0;
        }
        if (w == 0)
        {
            sw = 0;
        }
        if (w == width - 1)
        {
            ew = 0;
        }

            // Calculate averige
            // Iterate over height
            for (int hi = sh; hi < eh; hi++)
            {
                // Iterate over width
                for (int wi = sw; wi < ew; wi++)
                {
                    // Add up the value of the 10 pixels
                    blue = blue + temp[h - hi][w - wi].rgbtBlue;
                    green = green + temp[h - hi][w - wi].rgbtGreen;
                    red = red + temp[h - hi][w - wi].rgbtRed;
                }
            }

I have tested everything I can think. Is it time hat my approach will not work in general and I need to go back to the drawing board?

~/pset4/filter/ $ ./filter -b images/tower.bmp t.bmp

helpers.c:185:39: runtime error: index -1 out of bounds for type 'RGBTRIPLE [width]'

helpers.c:186:41: runtime error: index -1 out of bounds for type 'RGBTRIPLE [width]'

helpers.c:187:37: runtime error: index -1 out of bounds for type 'RGBTRIPLE [width]'

helpers.c:185:39: runtime error: index -1 out of bounds for type 'RGBTRIPLE [height][width]'

helpers.c:186:41: runtime error: index -1 out of bounds for type 'RGBTRIPLE [height][width]'

helpers.c:187:37: runtime error: index -1 out of bounds for type 'RGBTRIPLE [height][width]'

Answer 1

As pointed out in the comment by curiouskiwi

It's saying that sometimes, h-hi is -1 and sometimes w-wi is -1 and you can't have negative indices into your array.

The mistake was that

temp[h - hi][w - wi]

should be

temp[h + hi][w + wi]