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    <p><code>const</code> at the end of a function signature means that the function should assume the object of which it is a member is <code>const</code>. In practical terms it means that you ask the compiler to <em>check</em> that the member function does not change the object data in any way. It means asking the compiler to check that it doesn't directly change any member data, and it doesn't call any function that itself does not guarantee that it won't change the object.</p> <p>When you create a <code>const</code> object you are asking the compiler to make sure that that object does not change beyond its initialization. That in turns means that the compiler will check you don't directly change its member data and that you don't call any function that does not guarantee it won't change the object.</p> <p>This is all part of the <strong>const correctness</strong> philosophy. In essence it means that if things work right now and they won't change then they will never break. In other words, constant things are easier to work with reliably. This <code>const</code> thing at the end of function signatures is a tool for you to prohibit things from breaking. This in turns means you should put <code>const</code> everywhere you possibly can.</p>
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    1. COthanks for this explanation. are there any arguments against using const in a function that doesn't change the object? I feel that software could get less flexibly maintainable if you suddenly decide for example to change some design and need to call a non const function in a currently as const declared function and then maybe a big chain of functions that call this function have to be changed too
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    2. CONo, there is no argument against using a `const`. That is, unless you know right now, at the time of designing your class, that a member function should be allowed to change the object. It's a design question that you should ask yourself early on, and it should easy to answer. It's not about "leaving the door open for later". Rather, it's about whether the function **should** change the object or **should not** change it. It's a yes/no question, black or white, with nothing in between, and it should be easy to answer. Note: it's not about **may** it change the object, but **should** it.
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    3. COThis in turn means the const-correctness philosophy forces you early on to be very conscious about what each function does. It forces you to decide and be very clear about the raison d'être of each of the member functions. That's a Good Thing. What you're asking is to leave a door open for changing the raison d'être of a function, and that's a Bad Thing. You should only change **how** a function gets what it's meant to do done, not **what** it does. Think about the users of your API (which well be you yourself). Don't pull the rug off their feet!
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