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In this section of the course,
we'll learn about c++ functions.

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Functions allow us to divide
our programs into modular units

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of executable code and call and
reuse these units as we wish.

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Functions are very powerful
abstraction mechanism.

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You've already seen functions
defined. The main function that

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we've been using in every program.

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And you've also used some
functions such as getline and the

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c-style string functions, string
copy, string length and others.

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In this section, we'll
understand what functions are

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and why they're so useful.

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Then we'll look at
functions in detail.

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First, we'll see how to define
functions and create function

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prototypes that make our functions
useful anywhere in our code.

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As we've already seen, when we
call a function, we usually send

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information to the function.

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This information is sent in the
form of function parameters.

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We'll see how to define these
parameters and exactly how they work.

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Functions also usually return
some kind of information to us

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when they're done processing.

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For example, if we have a function
that calculates the square root of a

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number, well, that function expects
the number, and it will return to

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us the square root of the number,
which we can use however we wish.

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Functions can also
take many parameters.

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And in some cases, we want to
default the value of some of

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those parameters, so we don't
have to provide them every time.

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We'll learn how to set these
default values for parameters to

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make our code easier to write.

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Then we'll learn how to pass arrays
to functions, and how to work

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with them inside the function.

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I'll discuss references
in the next section.

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But we'll look at how we can
pass information to a function

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efficiently by avoiding copying.

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We'll also see how we can
change past information as

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well as protect it from change.

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Then we'll discuss inline functions.

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Inline functions are functions
that the compiler optimizes

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to avoid the overhead involve
when we call functions.

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Remember, when we use the auto
keyword to allow the compiler to

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deduce the type of a variable? Well,
we can also use the auto keyword

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to allow the compiler to deduce the
type of the function return value.

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This is pretty cool and it can
save us from writing a lot of

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unnecessarily complex code.

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Finally, we'll learn
about recursive functions.

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These are functions
that call themselves.

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You might be wondering why
would a function call itself.

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You'll see it's pretty cool
and it can help solve a class

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of problems that would be more
complex to solve without recursion.

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At the end of this section, we'll
do a challenge project, and we'll

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be well on our way to starting to
learn object-oriented programming.

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Let's get started.