If you don't want others (or yourself) to overwrite existing values, you can add the
in front of the variable type.
This will declare the variable as "constant", which means unchangeable and read-only:
const int myNum = 15; myNum = 20; // error
const keyword is useful when you want a variable to always store the same value, so that others (or yourself) won't mess up your code. An example that is often referred to as a constant, is PI (3.14159...).
Note: You cannot declare a constant variable without assigning the value. If you do, an error will occur: A const field requires a value to be provided.