C++ interview questions (3)

19. What is function template and class template?

Function templates are special functions that can operate with generic types.

template <class myType> myType GetMax (myType a, myType b) { return (a>b?a:b); } example: int a=GetMax(1,2); double b=GextMax(1.0,2.0);

Class template have members that use template parameters as types

template <class T>
class mypair {
    T values [2];
  public:
    mypair (T first, T second)
    {
      values[0]=first; values[1]=second;
    }
};

Example:

mypair<int> myobject (115, 30);

mypair<double> myfloats (3.03, 2.28);      20 .What is POLYMORPHISM and give an example using eg. SHAPE object: If I have a base class SHAPE, how would I define DRAW methods for two objects CIRCLE and SQUARE POLYMORPHISM : A phenomenon which enables an object to react differently to the same function call. in C++ it is attained by using a keyword virtual example public class SHAPE { public virtual void SHAPE::DRAW()=0; }; Note here the function DRAW() is pure virtual which means the derived classes must implement the DRAW() method. public class CIRCLE::public SHAPE { public void CIRCLE::DRAW() { // TODO drawing circle } }; public class SQUARE::public SHAPE { public void SQUARE::DRAW() { // TODO drawing square } }; 21. What is virtual function? Give an example to explain using/not using virtual function.   C++ virtual function is a member function of a class, whose functionality can be over-ridden in its derived classes.

#include<iostream>
using namespace std;

 class Window // Base class for C++ virtual function example
     {
       public:
          virtual void Create() // virtual function for C++ virtual function example
        //     void Create()

          {
               cout <<"Base class Window"<<endl;
          }
     };

     class CommandButton : public Window

     {
       public:
          void Create()
          {
              cout<<"Derived class Command Button - Overridden C++ virtual function"<<endl;
          }
     };

     int main()
     {
         Window  *x, *y;

         x = new Window();
         x->Create();

         y = new CommandButton();
         y->Create();
         return(0);
     }

If the function create  is declared virtual, the following output is given: 

Base class Window
Derived class Command Button - Overridden C++ virtual function

If the function create is not declared virtual, the following output

is given 

Base class Window

Base class Window

The base function create is kept calling.