Get pin input status without using the arduino library I am not allowed to use the Arduino Library (or any Library) for this program. How would I check the input of a pin? 

I found two different functions: 

In Arduino.h:

#define bitRead(value, bit) (((value) &gt;&gt; (bit)) &amp; 0x01)


Following digitalRead back to pgmspace.h:

#define __LPM_enhanced__(addr)  \
(__extension__({                \
    uint16_t __addr16 = (uint16_t)(addr); \
    uint8_t __result;           \
    __asm__ __volatile__        \
    (                           \
        "lpm %0, Z" "\n\t"      \
        : "=r" (__result)       \
        : "z" (__addr16)        \
    );                          \
    __result;                   \
}))


For the first one, I don't know where bit and value come from and I just don't understand the second one at all.
For reading, e.g., PB2, you would test

PINB &amp; _BV(PB2)


where PINB is the port input register and _BV(x) is a macro defined as
(1 &lt;&lt; (x)).

C.f. the datasheet for the relevant port names.

See also the Arduino tutorial on
port manipulation.