Make File

Do you know about makefile? 

lets say you have a large collection of c++ file to build an app, so every time you compile your code you have to compile all the file explicitly.
to solve this problem  makefile comes to rescue. in makefile you can provide instruction to build your project,  and specify to build only those file which you 
 have changed.  It makes build fast and save resources (CPU< MEMORY , etc ).