Update cv4/a_train.c

cv4/a_train.c

@@ -0,0 +1,18 @@
+#include "a_train.h"
+#include <stdio.h>
+
+struct car* add_car(struct car* first,const char* target) {
+    return NULL;
+}
+
+void print_train(struct car* first) {
+}
+
+void cancel_train(struct car* first) {
+}
+
+
+struct car* clear_train(struct car* first, const char* target) {
+	return NULL;
+}
+