Upcast the pointer for calculator to a base type to employ polymorphism

main.cpp

@@ -6,7 +6,7 @@
 
 int main()
 {
-    auto calc = std::make_unique<BaseCalculator>();
+    std::unique_ptr<BaseCalculator> calc = std::make_unique<SpecialCalculator>();
 
     std::cout << "Initializing calculator";