header files in C

Should you have to include a header file into its own library? I can't understand why I sometimes, but not always, get compile errors because it's not getting the header file prototypes before it compiles the libraries.

>>46
char tada[]="Tada!\n";
int t=write(stdout,tada,strlen(tada));
if(t==-1) write(stderr,"could not write to stdout!",26);
you fucking moron