C++ program to implement const objects and const functions :

Constantobj.cpp

    #include<iostream>

    using namespace std;

    class temp{
        public:
            void fn();
            void constantfn() const;
    };

    void temp::fn(){
        cout<<"Hello, Am an normal function."<<endl;
    }

    void temp::constantfn() const{
        cout<<"Hi, Am an constant function :P"<<endl;
    }

    int main()
    {
        // Normal Objects can call both normal and constant functions.
        temp x;
        x.fn();

        // Constant Objects can call only constant functions.
        const temp y;
        y.constantfn();

        int a=10;

        // Constant Pointer...
        int* const ptr=&a;
        cout<<"The value pointed by the constant pointer is "<<*ptr<<endl;

        int b=20;

        // Pointer to constant...
        const int* ptr2=&b;
        cout<<"The constant value pointed by the pointer is "<<*ptr2<<endl;

        return 0;
    }