For exemple I saw 'hey!' only when I close the executable.

To be clear, you're trying to run one of your executable from 4coder ?

Could this be similar to this issue: printf to buffer only appearing after buffer get to a size ?

Try adding fflush( stdout ); after the prints to make sure they go out to the screen.

Okay if I add fflush( stdout ); it work. But they is no other solution to just add fflush( stdout ); after each printf ?

You can disable buffering on stdout with this: