1. What is a pure virtual function?
Ans. A pure virtual function (or abstract function) in C++ is a virtual function for which we don’t have implementation, we only declare it. A pure virtual function is declared by assigning 0 in declaration. See the following example.
2. What is abstract class?
Ans. A class which contains atleast one pure virtual function, is known as abstract class. see the following example
in above example, Test is an abstract class because it has a pure virtual function.
Some interesting facts about abstract class
1) We can’t create an object of abstract class.
Compiler Error: cannot declare variable 't' to be of abstract type 'Test' because the following virtual functions are pure within 'Test': note: virtual void Test::show()
2.We can have pointers and references of abstract class type.
For example the following program works fine.
3. If we do not override the pure virtual function in derived class, then derived class also becomes abstract class.
The following example demonstrates the same.
Compiler Error: cannot declare variable 'd' to be of abstract type 'Derived' because the following virtual functions are pure within 'Derived': virtual void Base::show()
3. What is the output of this program?
Explanation: In this program, we are calculating the area of rectangle and
triangle by using abstract class.
4. What is the output of this program?
Explanation: In this program, We are executing these based on the condition given in array. So it is printing as 212.
5. What is the output of this program?
GeeksForGeeks is awesome
Explanation: In this program, We are combining the two statements from two classes and printing it by using abstract class.
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