AVR-Chat

hi,can anyone explain me the logic behind the pull up resistors in atmega 16.in which condition my input pin is in high impedance state? If i write

DDRA=0x00;
PORTA=0xFF; 

this means that i have enable the pull up resistor.so r the pins at +5V or floating input is there? secondly for testing d input do i need to use

char test;
test=PINA;
if(test == 0xFF)
{}

or do i use

bit_is_set(PINA,0) && bit_is_set(PINA,1) ,etc

or if i test logic 1 at A0 ,then is this app,

if((test & 0x01)==0x01)

basically i have 5 sensor input which are connected to A0-A4 and i need to test d input either it is 1 or 0 .