Constant Members in C++

In C++, a constant member is used to make a data member or function immutable. This means that once a value is set, it cannot be changed. This is an important programming concept, useful when the value of a piece of data or function should never be changed during the program.

Constant Data Member: A data member defined using the `const` keyword, whose value cannot be changed after being set. It must be initialized in the class's constructor.

Constant Member Function: A function declared with the `const` keyword. This function is not allowed to change any data member. It is used to prevent accidental modification of data members inside a function.

In C++, an object can also be declared as constant. This means that no data member of that object can be changed. A constant object can only call constant member functions.

In C++, if we want a specific data member of a constant object to be changeable, we can use the `mutable` keyword. A mutable data member is a special type that can be changed even inside constant functions.