//=============   A simple program to demonstrate the use of "const" keyword with pointers==================
/*
*    By => Bipin Gosain
*    Date => 17/4/2016
*/
#include <iostream>
 
 int main(){
     using std:: endl;
     using std:: cout;
     //========= Part I ===========
     /*
         int data = 100;
         const int *pointerToAConstValue = &data;//A pointer to a constant value
        *pointerToAConstValue = 1;//Error 
         data = 1;//No error
     */
     //========= Part II ===========
        /*
        const int data = 100;//constant value
        const int *pointerToAConstValue = &data;//A pointer to a constant value
        *pointerToAConstValue = 1;//Error 
        data = 1;//Error
        */
    //========= Part III ===========
        int data = 100;//constant value
        int anotherVariable = 200;
        int * const pointerToAConstValue = &data;//A constant pointer ...it can't point to any other location(Address)
        *pointerToAConstValue = 20;//No Error
        cout << "value at pointer "<< *pointerToAConstValue << endl;
        data = 1;//No Error
        cout << "value at pointer "<< *pointerToAConstValue << endl;
        pointerToAConstValue = &anotherVariable;//Error
     
 }

Following program is to demonstrate the use of const keyword with pointers:

PART I : shows  the pointer to a constant value which can't be changed by the pointer but can be changed directly.

PART II : shows a constant value being pointed which cannot be changed by the pointer or directly.

PARTIII : shows the use of constant pointer which cannot point to any other variable expect to which it is pointing.