How to compare strings of two files?

How to compare strings of two files?

I am a new c-language programmer.
I have got two files. One consists of lines like:
84:1b:5e:a8:bf:7f
00:8e:f2:c0:13:cc
Another consists of lines like:
00-22-39
8C-FD-F0
My question is how can I using C language compare first half of line in
the first file with a line in the second file? Like: is 84:1b:5e equals to
8C-FD-F0? I know the way to create an arrays to store those lines for the
further comparison. But do I really need to create arrays?
P.S: comparison is case-insensitive