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.

>>47

char tada[]="Tada!\n";
if(write(stdout,tada,strlen(tada))==-1 && write(stderr,"could not write to stderr!\n",27)==-1) exit(255);
you fucking moron