Finding all the points within a circle in 2D space

Question

I am representing my 2D space (consider a window), where each pixel is shown as a cell in a 2D array. i.e. a 100x100 window is represented by the array of same dimensions.

Answer 1

If the following is true:

( ( xPos - centreX)^2 + (yPos - centreY)^2 ) <= radius^2

where xPos and yPos are the coordinates of a point you're checking, then the point is inside your circle.