How to deal with hexadecimal values

[king4ever101]

hi
i write a programe to convert the ascii to hexadecimal then i want to write a function to deal with these hexadecimal value>>>> for better explain here is an exapmle:
if i have these hexadecimal value 44 2A 66 E2 F6 77
so i want to write a function that look to first character (44) to see what the values around it (before it and after it) and replace it is value depend on that such that replace the (44) with another value like (54) and then go to the next value(2A) and see the values before and the value after >>>>>
which mean for example if it is found that the value before the value (2A) is (44) and the value after it is (66) replace it with (77) and if it found that the value before it is (E2) and the value after is (66) replace it with (F3) and so on.....
and second problem how to make the function to see the the values as two bit not bit by bit which mean to look to the value 44 and then to 2A and so on not to look to each bit (see 4 then 4 then 2 then A)
i hope you understand the idea
and sorry for my english