Add example for classic singleton

cpp/patterns/singleton/singleton-pointer.cpp

@@ -0,0 +1,11 @@
+
+#include "singleton-pointer.hpp"
+
+// Initialize pointer to instance to null; Allocate on first call to getInstance
+ClassicSingleton* ClassicSingleton::instance = nullptr;
+
+ClassicSingleton* ClassicSingleton::getInstance(){
+  // If the instance is null, return a new one; Otherwise return instance
+  if(instance == nullptr) instance = new ClassicSingleton;
+  return instance;
+}