Can you explain what an abstract class is and how it differs from a regular class?

An abstract class is a class that is not intended to be instantiated directly, but serves as a base for other classes. In C++, an abstract class is defined by having at least one pure virtual function.

Differences between an abstract class and a regular class:

• You cannot create an object of an abstract class directly.
• It contains at least one pure virtual function, which must be implemented by derived classes.
• It is used to define an interface and common functionality that subclasses should inherit.

Example:

class AbstractBase {
public:
    virtual void doSomething() = 0; // pure virtual function
};

class Derived : public AbstractBase {
public:
    void doSomething() override {
        // implementation
    }
};

// AbstractBase obj; // error, cannot create an object of an abstract class
Derived d; // correct