use stderr if getline fails

factorial_examples/factorial.c

@@ -25,7 +25,7 @@ int main(void) {
 	fputs("Enter number to factor: ", stdout);
 	int err = getline(&lineptr, &bufsize, stdin);
 	if(err == -1) {
-		puts("Error reading line from user input");
+		fputs("Error reading line from user input\n", stderr);
 		return 1;
 	}