const attribute makes whole element const?

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I had never problems with that in C++.
If I have members which are const because they are assigned only 
one time and needs no other assignment, why should I declare this 
member not as const?

In the example I know exactly that I assign only one time a name 
to this struct, so why I should not declare it as const?

Other example: you have a unique birthday date. This is const you 
cannot change it like a name or a telephone number. So if you 
have a Person struct which holds any data of a single people, you 
won't declare the date as const? I would. And I had expected that 
this is normal behaviour.