Of course you can, the 18F4550 had analogue inputs, as do many PIC's - the datasheets explain how to use them, or you might consult my tutorials for 16F examples, which are probably quite similar?.
I want to use yhe 18f beacause the charger is a part of more complex project and i need a beter microcontroler.What is your recommend,lern toprogram this pic in C or ASM?
C, definitely. There is a free version of MPLAB IDE & C18 compiler for download at Microchip's site. It is a 6 month 'trial' version but I believe is fully featured.
I want to use yhe 18f beacause the charger is a part of more complex project and i need a beter microcontroler.What is your recommend,lern toprogram this pic in C or ASM?
Because the application notes are in C, I would suggest learning many C, and (as already mentioned) MicroChip provide a free C compiler for it - it's fully featured, but after a trial period some of the optimisations are disabled.