How to calculate sprite coordinates by index in a sprite-sheet with fixed-sized sprites.

gistfile1.c

// These are known beforehand
int imageWidth = 640;
int imageHeight = 480;
int tileWidth = 32;
int tileHeight = 32;

int tilesPerRow = imageWidth / tileWidth;

int index = 5;

int left = tileWidth * (index % tilesPerRow);
int top = tileHeight * (index / tilesPerRow);
int bottom = top + tileHeight;
int right = top + tileWidth;