Some quick and dirty C code for converting from cartesian to polar coordinates.
dist = sqrt( deltaX * deltaX + deltaY * deltaY );
angle = acos( deltaX / dist );
if( angle < 0 )
angle = -angle;
else if( deltaX <=0 && deltaY < 0 )
angle=-angle;
else if( deltaX < 0 && !(deltaY <= 0) )
angle=-angle;
And the other way:polar to cartesian
newX = dist *
cos ( angle );
newY = dist *
sin ( angle );