a Bit of confusion (haha - Pun)

I'm confused with Bits. I know they are arbitrary as far as length goes which leads to my confusion.

I'm reading Applied Cryptography (Schneier), and i'm confused as to the size of such things, well not bits i guess but like bytes maybe. I know a char or int on the computer is 8 bits right? Like how would i implement something if i needed, suppose a 4 bit variable?

And how can i manipulate the bits on a bit-by-bit basis?

Thanks!

It is hard to find a computer where the int is 8 bit length... Or even impossible - because C-standard require int to be big enough to store 32767 witch require at lease 16 bits

char is AT LEAST 8 bits long, can be longer...

for storing 4 bit value you can use or char with masking (you can be sure that you have your 4 bits there, the rest is just ignored) or you use bit-fields making a compiler to chose the appropriate container for it