drawing a line

hey guys,

i have a 2 dimensional array that im using as a canvas on which to 'draw' lines and things on. the problem i had was that i wasnt able to construct an algorithm that would actually draw this line. i found Bresenham's line algorithm and implemented it into my solution. the only problem is that the algorithm only works for lines that are across the X axis, if you have a line that is vertical (or close enough to it) the resulting line will only have as many points in the y axis as it does in the x axis.

heres the algorithm:
// Start
void Bresenham(int x1, int y1, int x2, int y2)
        {
            int slope;
            int dx, dy, incE, incNE, d, x, y;
            // Reverse lines where x1 > x2
            if (x1 > x2)
            {
                Bresenham(x2, y2, x1, y1);
                return;
            }
            dx = x2 - x1;
            dy = y2 - y1;
            // Adjust y-increment for negatively sloped lines
            if (dy < 0)
            {
                slope = -1;
                dy = -dy;
            }
            else
            {
                slope = 1;
            }
            // Bresenham constants
            incE = 2 * dy;
            incNE = 2 * dy - 2 * dx;
            d = 2 * dy - dx;
            y = y1;
            // Blit
            for (x = x1; x <= x2; x++)
            {
                putpixel(x, y);     // <- being the function that actually sets the pixel
                if (d <= 0)
                {
                    d += incE;
                }
                else
                {
                    d += incNE;
                    y += slope;
                }
            }
        }

// End

now im guessing the problem is in the loop, its checking through the x values, however if its a vertical line, well then there will only be one x value, therefore only one point will be drawn.

i've thrown in the following:

//Start
      // Check to see if we have a vertical line
      if (dx == 0)
      {
            // Line is vertical, draw it
            for (y = y1; y <= y2; y++)
            {

                  // Start drawing
                  putpixel(x, y);

            }

                  // Exit Function
                  return;

      }
// End

...up near the top of the function that caters for if the line is exactly vertical, however it doesnt cater if the lines a couple of degrees off.

i've been trying to modify the code, however so far i havnt had much luck. has anyone ever used something like this before? or would know how i can change it to allow me to draw vertical?

thanks