I have no corners.

I have 2 long sides, 2 short sides and 4 corners.

I have 3 straight sides and 3 corners.

I have 2 curves on top and 1 corner at the bottom.

I have 4 straight sides and 4 corners. All sides are of the same size.

I have 4 equal sides like a square, but I stand on one of my corners.

I have 5 pointed corners.

Just like circle, I have no corners.