is const (c++) optional?

Question

according to some tutorials i read a while back, the \"const\" declaration makes a variable \"constant\" ie it cannot change later.
But i find this con

Answer 1

Its always optional. If its all your code sure you can forget it ( I wouldn't recommend it, because it protects you), but when you interact with others, you're essentially providing a contract for them that you won't change their object or calling a function does not change the state of your object. This can be invaluable when you are not familiar with other's code, or you don't have the source.