It sounds like you have three distinct problems:

How to read a text file with C
How to write a text file with C
How to process a stream of data

Fortunately for you, you have internet access and there are a *ton* of
resources for C programming on the internet.

Reading a file can be as simple as
http://www.phim.unibe.ch/comp_doc/c_manual/C/EXAMPLES/read_file.c
Writing is not much more work, using a command such as fputc on an open
(for writing) file handle:
http://www.phim.unibe.ch/comp_doc/c_manual/C/FUNCTIONS/fputc.html

A C reference is here
http://www.phim.unibe.ch/comp_doc/c_manual/C/cref.html

As far as processing the file itself, there are a number of ways to
attack it.  If you knew the file was well-defined, and would never have
any sequence other than '111' and '000' then you could simply

top:
read a character into variable c
Write from c into the output file
read a character into variable c
read a character into variable c
goto top

It's cheating, in a sense, but whether it's acceptable depends on your
data.  You didn't tell us what your program needed to do in the case
that there are only two 1's, 0's, or a single 1 or 0 - whether those are
output as well, or cause a error to be displayed, or ignored, etc.

I could go on with many, many solutions, but none of them may work, or
all of them may work.  I can't tell, since you haven't given us a
complete specification.

Also- read up on the use of eof().  It's important to know when the file
ends and stop reading from it.

-Adam

ali dawji wrote:

> Dear Sir.
> I am a new beginner in c language, and I have a problem as follow:
> I have a file (f1.txt) with data for example:
>
> 000111111000111000000000111111000???
>
> I want to read this file and save the result in other file, called
> (f2.txt),
> the reading procedure is as follow:
> 1-every three zeros change to one 0.
> 2-every three ones change to one 1.
> So the result of the file (f2.txt) should be as:
> 01101000110?
>
> Any help is welcomed.

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