feat(topic): add virtual functions topic content (#8497)

src/data/roadmaps/cpp/content/virtual-methods@hNBErGNiegLsUJn_vgcOR.md

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+# Virtual Functions in C++
+
+Virtual functions enable runtime polymorphism in C++, allowing derived classes to override base class behavior. When called via a base pointer/reference, the *actual object's type* determines which function is executed (dynamic dispatch). Non-virtual functions use compile-time resolution based on the pointer/reference type (static dispatch), which prevents overriding.
+
+```cpp
+// Base class with virtual function
+class Animal {
+public:
+    virtual void speak() { std::cout << "Generic sound"; }
+};
+
+// Derived class override
+class Dog : public Animal {
+public:
+    void speak() override { std::cout << "Woof!"; } // Dynamic dispatch
+};
+```
+
+Visit the following resources to learn more:
+
+- [@official@C++ Virtual Functions Documentation](https://en.cppreference.com/w/cpp/language/virtual)
+- [@article@GeeksforGeeks Virtual Functions Guide](https://www.geeksforgeeks.org/virtual-function-cpp/)
+- [@video@Virtual Functions Explained (YouTube)](https://www.youtube.com/watch?v=oIV2KchSyGQ&ab_channel=TheCherno)