electric field due to plane sheet

When you write the gauss law, which states that for a conductor

 

Qenclosed = integral (E.dA)

then, since the direction of the electric field due to the infinite plane sheet would be perpendicular to it always, so the E.dA = 0 as E and dA would be perpendicular to one another for the infinite sheet. (dot product of 2 perpendicular vectors = 0)

 

However, at the ends of the cylinder, the E.dA = EA as E and A would have the same direction.