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Okay, so welcome to the
section 9 challenge.

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This challenge puts together
just about everything we've

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learned to solve a problem.

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I mean the section 9 workspace
under the challenge project.

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There's also a challenge solution
project, which includes my

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solution which I'll cover in
the video right after this one.

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Let's talk about the challenge
and then I'll give you a

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demo of the running solution.

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This challenge is about using a
collection or a list of integers

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and allowing the user to select
a few options from the menu.

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So here's the menu,
p-a-m-s-l-q are the selections.

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If the user presses p, you
print the elements of the list.

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If they press a, you add a number
to the list, which you ask them for.

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If they press m, you display the
mean of the numbers in the list.

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S and l, the smallest number
and the largest number.

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And of course, if they
press q, you quit.

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Now anything else, you should tell
them invalid choice and so forth.

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Okay, just like we've been doing.

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So let's go over a little
bit more of the detail here.

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We're only accepting valid
choices from the user, both

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uppercase and lowercase
selections should be allowed.

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And if they enter an illegal
choice, you should say unknown

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selection, please try again,
and then redisplay that menu.

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Okay, If the user enters a
upper or lowercase p, we display

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all the elements of the list.

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Remember, this is a list of integers.

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If the list is empty, you should
just display two square brackets

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and then say the list is empty.

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If the list is not empty, then all
the list elements, all the integers in

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that list should be displayed inside
square brackets separated by spaces.

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So in this case, the list has
the integers 1 2 3 4 and 5., and

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this is how we'll display them.

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If the user enters an uppercase
or lowercase a, then you'll prompt

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them for a number to add to the
list in which case you add it.

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And then you display whatever
number they entered added.

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Okay.

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It's okay to have duplicate
entries in the list.

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And the last couple are
pretty straightforward.

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If they press m upper or lower
case, you basically iterate

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through that list and calculate
the average of the list or the

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mean of the list and display that.

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If the list is empty, obviously
you can't calculate the means,

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you simply display unable to
calculate the mean no data.

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For s, again upper or lower
case, you basically iterate

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through the list and find the
smallest integer in that list.

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And that's what you
display back to the user.

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So in this case, if the list
contains 2 4 5 1, you'll display

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the smallest number as one.

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If the list is empty, you should
display unable to determine

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the smallest number because
obviously the list is empty.

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L works the same way except
you're looking for the

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largest element in the list.

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When they press q, you say goodbye,
and the program terminates.

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Okay, so that's the challenge.

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Before you begin, write out the steps
you need to take and decide you know

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what order you should do them in.

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Think about the loops.

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You know.

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You need loops you know your if
statements or switch statements.

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Think about what the
best way to do this is.

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Start small, build little pieces,
test those little pieces and then

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add as you go and test as you go.

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One big hint, use a vector.

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I mean don't use an array here.

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Use a vector, I should be
pretty obvious because we want this to grow dynamically.

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A couple of more things.

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You could add functionality once
you finish this basic challenge

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to search for a number in the list.

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And if it's found, how many times did
it occur, maybe it's not in the list.

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The vector class has a
.clear method that you can

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call to clear out the list.

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So maybe you want to you know
have an option for the user to

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delete everything in the list.

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Maybe you want to not
allow duplicate entries.

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So if I press to enter the
number 5, you'll let me enter it.

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If I want to enter it again, you'll
say sorry it's already in the list.

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So come up with your own ideas.

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It's really all about
learning and practice.

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Okay, so let me give you
a sample run of this.

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So here's the menu.

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As you can see p is print, a is
add, m is mean, s is smallest,

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l is largest and q is quit.

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Let's do the obvious one.

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First, let's press q, we're out.

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It says goodbye.

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Our program is over.

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Okay, so let me run it again, and
let's print the numbers in the list.

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Right now the list is empty.

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So if i press p.

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And again, it could be uppercase or
lowercase, you get the two square

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brackets and the list is empty.

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Now I want to add a number.

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I'll press a.

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Let's say I want to add the number
10 to the list, 10 is added.

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And let's say I want to add another
number, so I'll press a again and I

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want to add negative 10 this time.

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So we've added negative 10.

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If I want to print the
numbers again, I'll press p.

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And there's my list
10 and negative 10.

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I'll add a couple of more, so
let's add 100 and let's add 500.

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And we'll display the
list again with a p.

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And now we've got 10, negative 10 100
and 500, just like what we thought.

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Display the mean of the
numbers, we'll press m.

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In this case, the mean is 150.

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Let's add another number.

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Let's add three and do the mean again.

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You know notice it's 120.6,
so the mean should be a

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double, not an integer.

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Finally, we'll do let
me print the list again.

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We've got 10 negative 10, 100 503,
the smallest should be negative

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10 and the largest should be 500.

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So let's test that out.

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I'll press s for the smallest.

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The smallest number is -10.

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And I'll press l for the
largest, the largest number is

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500, exactly what we expect.

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And of course if the user types in 1,
unknown selection please try again or

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if they press o if they press anything
that's not one of these letters, we

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tell them unknown selection redisplay
the menu and grab the input from them.

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Again, press q to quit.

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That's it.

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That's the challenge.

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As I said, this can be a tricky
little challenge to do because

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you've got a lot of things going on.

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You've got loops and loops
within loops and if statements

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and maybe switch statements and
maybe do loops maybe while loops.

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It's really up to you to
decide how to solve it.

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Give it a shot.

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Don't be discouraged if it takes you
more than a few attempts to get it.

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That's pretty normal.

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I'll see you in the next video.

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We'll go over my solution to it
or at least one solution to it.

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All right, good luck.