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KwickClips Cyber Safety and Ethics · 42 sec · free

What makes a class abstract?

Short answer. At least one pure virtual function.

Can you make a pointer to it?

Yes.

Remember

= 0 means pure virtual
Abstract: no objects
Derived class overrides it

Shape s gives a compile error. Why? Area equals zero is a pure virtual function. A class with one is abstract. So we cannot create its objects. Equals zero means pure virtual. Abstract means no objects. Derived classes override it.

This clip is from the full lesson: Polymorphism and Virtual Functions — 7 minutes, with the tables, the quick answers and the whole lesson in text.

Useful for: Programming All levels C++

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Table comparing compile time and run time: binding, uses, speed.Is overloading compile time or run time?40 secC++ struct B with operator+ returning B{a + x.a}, t{10} + v{25} gives 35.What is the function named?41 secC++ code struct Shape with virtual void draw, struct Circle overriding draw, Shape *p = &c; p->draw();Where is virtual written?40 sec
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