Help for my first program, first post!

Hi guys (and girls!),

Need some help for my program (C IN UNIX Environment)

Basically I want to have a C program which, for an existing file supplied by the command line argument (E.g. File1.txt) replaces all the occurrences of the words �We� or �we� by �I�; �a� by �the�; and �A�
by �The�. Then print the replaced file. All other characters of the file are to be left unchanged.

I know basically to change a string of characters you use:
String.Replace("oldval","newval");

How would you go about doing this to an entire txt file???

I was told by more experienced ppl I may have to use read, write, open, lseek commands.

Sorry for those of you who think this is ezy, just learning and any help is great!!

Thanks....