Preventing the modification of a value

The essential point of immutability is preventing value modification. In C++ programming language, there is a keyword to prevent the code modifying a value. The keyword is const and we are going to use it in the const.cpp code. We have a class named MyAge which contains a public field named age and we set it as const. We will play with this const field and the code will look like following:

    /* const.cpp */
    #include <iostream>

    using namespace std;

    // My Age class will store an age value
    class MyAge
    {
       public:
         const int age;
         MyAge(const int initAge = 20) :
          age(initAge)
         {
         }
     };

    auto main() -> int
    {
      cout << "[const.cpp]" << endl;

      // Initializing several MyAge variables
      MyAge AgeNow, AgeLater(8);

      // Displaying age property...