'SIGHUP','SIGTSTP' undeclared

I compile following statement

signal(SIGHUP,sig_hup);
kill(getpid(),SIGTSTP);

$gcc test.c
it raise following error:
error:'SIGHUP' undeclared (first use in this function)
error:'SIGTSTP' undeclared (first use in this function)

Why raise above error? which head file include 'SIGHUP','SIGTSTP' define?

Thanks

#include <signal.h>