diff --git a/lcthw/ex13.c b/lcthw/ex13.c
index 049c254..128612b 100644
--- a/lcthw/ex13.c
+++ b/lcthw/ex13.c
@@ -11,13 +11,14 @@ int main(int argc, char *argv[])
 
 	// let's make our own array of strings
 	char *states[] = {
-		"California", "Oregon",
-		"Washington", "Texas",
+		"California",
+		"Oregon",
+		"Washington",
+		"Texas",
+		NULL,
 	};
 
-	int num_states = 4;
-
-	for (i = 0; i < num_states; i++) {
+	for (i = 0; states[i] != NULL; i++) {
 		printf("state %d: %s\n", i, states[i]);
 	}