The terminal driver will still think your shell is the foreground process.

So while your shell creates a "foreground" process to run a program, a SIGINT signal from the keyboard will be sent to the shell!

The signal handler should "forward" this signal to the process that the shell considers as the "foreground" process.

How, by using the kill function to send the SIGINT signal to the foreground job; that is, to the the whole process group.