diff --git a/ex22.h b/ex22.h
new file mode 100644
index 0000000..bc894b0
--- /dev/null
+++ b/ex22.h
@@ -0,0 +1,16 @@
+#ifndef _ex22_h
+#define _ex22_h
+
+// makes THE_SIZE in ex22.c available to other .c files
+extern int THE_SIZE;
+
+// gets and sets an internal static variable in ex22.c
+int get_age();
+void set_age(int age);
+
+// updates a static variable that's inside update_ratio
+double update_ratio(double ratio);
+
+void print_size();
+
+#endif