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In this short video, we'll see how
the const qualifier affects pointers.

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We've already seen that the
use of const with function

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reference parameters essentially
makes them read-only.

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In c++, we can qualify a
pointer in several ways.

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First, we don't have
to use const at all.

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In this case, we have a pointer just
as we've been using up to this point.

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We can change the data the
pointer is pointing to, and we

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can change the pointer itself
and make it point somewhere else.

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The const qualifier gives us
more fine-grained control of

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what we allow to be changed.

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We can have pointers to
constants, constant pointers and

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constant pointers to constants.

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These will be very useful
when we pass pointers to

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functions in the next video.

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Let's take a look at each one of them.

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In the case of pointers to constants,
the data pointed to by the pointer

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is constant and can't be changed.

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However, the pointer itself
can change and point elsewhere.

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Let's take a look at this example.

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We have two integers
declared and initialized.

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These are high score and low score.

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But this time when we declare the
pointer, we use the const qualifier

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before the type that we point to.

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So score pointer is a pointer
to an integer constant, and we

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initialize it to point to high score.

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If we attempt to change the
value of the point to two

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data, in this case, high score,
we'll get a compiler error.

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However, we're free to assign another
address to the pointer and have

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it point somewhere else as we do
in the last assignment statement.

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In the case of constant pointers, it's
the pointer itself that's constant.

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So the data pointed to by the pointer
can be changed via the pointer.

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However, the pointer itself
cannot be changed and can't

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point to anything else.

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Notice that we still use the
const qualifier, however, we

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use it before the asterisk
in the pointer declaration.

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So we're declaring score pointer
as a const pointer to integer.

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All right, let's look
at the last case.

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In this case, it's a constant
pointer to constants.

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We need to use the const qualifier
twice in the pointer declaration.

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So the data pointed to by the
pointer is constant and can't

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change, and the pointer itself is
also constant and can't change.

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Notice the syntax, score
pointer is a constant pointer

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to an integer constant.

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In this case, if we try to
modify either the data or the

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pointer, we get compiler errors.

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The const qualifier is very
useful and it's often used when

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passing pointers to functions.

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We'll see that in the next video.