Simple Issues

[Wilhelm Korrengk]

Hello,
I`m pretty new to this list and there are some things I`d be happy to know ;o)

I plan to check large numbers with several rithims whether they are primes or 
not. 

Can I just define a huge int and use it in for() or if?
Can I build a library of my functions load them into delphi sending strings 
with high numbers to the funktions which understand them as they were ints?

(If yes; How? I`m really missing an easy tutorial on it)

Thanks in advance!
Wilhelm K.