If you have a static variable that never changes and you want that nobody overrides your variable, use the const keyword by declaration. It makes the variable unchangable (constsant).

For example:

const double x = 42;

The variable x will always be 42 and nobody can change it. The following code would cause an error:

const int x = 10;
x = 15;

You should declare variables as constants if you are sure that they will probably never change:

const int monthPerYear = 12;
const char firstAlphabetLetter = 'A';