add example of state pattern in C++

cpp/patterns/state/state.cpp

@@ -0,0 +1,13 @@
+
+#include "state.hpp"
+
+// Delegate calls from State->changeState to Car->changeState
+void State::changeState(Car *c, State *s) { c->changeState(s);}
+
+// Stopped state transitions
+void Stopped::Start(Car *c) { changeState(c, Running::instance());}
+void Stopped::Smash(Car *c) { changeState(c, Broken::instance());}
+
+// Running state transitions
+void Running::Stop(Car *c) { changeState(c, Stopped::instance());}
+void Running::Smash(Car *c) { changeState(c, Burning::instance());}