All port pins are forced to high state after a reset.
Hence always set up the port pins so that they read "0" or low when you press the button.

It is called Active Low input.Once you read the pin invert it in software. This is the right way to do it.

And with most derivatives ( refer the data sheet ) port pins are pulled high strongly when used as inputs - so you dont have to worry about your pull resistors ( generally ).

Raghu