/* poor programming practice */
temp = box_x1;
box_x1 = box_x2;
box_x2 = temp;
temp = box_y1;
box_y1 = box_y2;
box_y2 = temp;
A better version would be:
/*
* Swap the two corners
*/
/* Swap X coordinate */
temp = box_x1;
box_x1 = box_x2;
box_x2 = temp;
/* Swap Y coordinate */
temp = box_y1;
box_y1 = box_y2;
box_y2 = temp;