If you don’t want others (or yourself) to overwrite existing values, you can add the const keyword 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
When you do not want others (or yourself) to change existing variable values, use the const keyword (this will declare the variable as “constant”, which means unchangeable and read-only):
const int myNum = 15; // myNum will always be 15
myNum = 10; // error: assignment of read-only variable 'myNum'
You should always declare the variable as constant when you have values that are unlikely to change: Continue reading C++ Constants