#include <iostream>
using namespace std;

int main(){

    int a = 10;
    int b = 100;

//
    int * ptr1 = &a;
    *ptr1 = 20;
    cout << "ptr1: "<<  *ptr1 << endl;
    ptr1 = &b;
    cout << "ptr1: "<< *ptr1 << endl;


//
    a = 10;
    b = 100;
    const int * ptr2 = &a;
    //*ptr2 = 20; // error
    ptr2 = &b;
    cout << "ptr2: "<< *ptr2 << endl;

//
    a = 10;
    b = 100;
    int * const ptr3 = &a;
    *ptr3 = 20;
    //ptr3 = &b;// error
    cout << "ptr3: "<< *ptr3 << endl;

//
    a = 10;
    b = 100;
    const int * const ptr4 = &a;
    //*ptr4 = 20; // error
    //ptr3 = &b;// error
    cout << "ptr4: "<< *ptr4 << endl;

}