void print_students(slist *head){
	clist * head_c;

	if(!head) {
		printf("STUDENT LIST: EMPTY!\n");
		return;
	}
	else{
		printf("STUDENT LIST:\n");

		while(head){
			printf("%d:%s\n",head->info->id,head->info->name);
			head_c=head->info->courses;
			if(!head_c)
				printf("student is not registered for courses.\n");
			else{
				printf("courses: ");
				while(head_c){

					printf("%d-%s",head_c->info->number,head_c->info->title);
					head_c=head_c->next;
					(!head_c?printf("\n"):printf(", "));
				}
			}
			head=head->next;
		}
	}
}
void print_courses(clist *head){
	slist * head_s;

	if(!head) {
		printf("COURSE LIST: EMPTY!\n");
		return;
	}
	else{
		printf("STUDENT LIST:\n");
		while(head){
			printf("%d:%s\n",head->info->number,head->info->title);
			head_s=head->info->students;
			if(!head_s)
				printf("course has no students.\n");
			else{
				printf("courses: ");
				while(head_s!=NULL){

					printf("%d-%s",head_s->info->id,head_s->info->name);
					head_s=head_s->next;
					(!head_s?printf("\n"):printf(", "));
				}
			}
			head=head->next;
		}
	}
}