How to use pure virtual function in C++

 #include<iostream>   //header file

using namespace std;      // header file

class shape    // creating class of name shape

{

protected:    // access specifier

float dim;    // protected variable of data type float of name dim is declared

public:      // access specifier

void getdim()        // member function in public access specifier

{

cin>>dim;       

}

virtual float caldata()=0;     // pure virtual function declaration

};     //end of class shape  (end of class should be by the semicolon)

class square: public shape    //class square derived from class shape  

{

public:      // access specifier

float caldata()       // function definition

{

return dim*dim;      //function body

                }

};   //end of class square

class circle: public shape    //class circle derived from class shape 

{

public:     // access specifier

float caldata()        // function definition

{

return 3.14*dim*dim;   //function body

}

};  //end of class circle

int main()

{

square s;        // object created of class square

cout<<"Enter length: "<<endl;       // prints enter length statement

s.getdim();    // getdim function called of class square

cout<<"Area of square: "<<s.caldata()<<endl;    // prints Area of square and the value of s.caldata() function

circle c;    // object created of class square

cout<<"Enter radius: "<<endl;   //prints Enter radius statement and 

c.getdim();    // getdim() function called of class circle

cout<<"Area of circle: "<<c.caldata()<<endl;   //prints area of circle and the value of caldata() function

}

Output:

Enter length:

23

Area of square: 529

Enter radius:

11

Area of circle: 379.94