for my research, I modify the C code that makes the PHP (not the code that is written with PHP but that which actually makes PHP). I want some way of compiling it and making it work with apache. How do I do that?
The manual is your friend:
http://www.php.net/manual/en/install.unix.apache2.php
./configure --with-apxs2=/usr/local/apache2/bin/apxs --other-options
make
make install