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SPEAKER: Let's talk about water.

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In this problem, we're going to
ask the user how many minutes they

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spent in the shower.

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From there, we're going to
estimate the amount of water

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that they used returning
it to them using

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water bottles as a unit of measurement.

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Hopefully, after seeing how many water
bottles they used in their shower,

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they'll start to conserve
a little bit more water.

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So let me break this problem
down into three todos.

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Your first task is to prompt and
validate the user for their input.

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Second is to calculate the
equivalent number of bottles

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that their shower used.

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And lastly, you want to
print that number out.

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So your program might
look something like this.

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After including the
appropriate libraries,

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your main function will
first have a section of code

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that prompts the user for the
minutes they spent in the shower.

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Then you'll have a section of
code that calculates and outputs

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the equivalent number of bottles used.

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Let's talk about user input first.

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The get_int function is a
function in the CS50 library.

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This function ensures that the
user will input an integer.

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We use the function by passing
in a prompt as a string.

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If the user follows that prompt
but does not enter an integer,

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then that user will be re-prompted
until they provide us with an integer.

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So just simply getting an
int might look something

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like this, where I call
the get_int function

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and ask the user to give me a number.

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Notice that the top that because
get_int is a safety library function,

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we must #include its declaration.

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Next, you'll notice where I
have given the user a prompt.

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But even though get_int
returns an integer,

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how can we actually keep track of
the integer inputted by the user?

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Here's where I'll introduce a variable.

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Let's call it n, where
in the variable n I'll

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store the result of getting
that integer from the user.

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Now, take a moment to pause
this video and perhaps

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write that code for
yourself so that you know

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how to get an integer from the user.

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Once you're ready, let's move on to
validating the input from that user.

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Because even though we have ensured that
we've gotten an integer from the user,

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what if they give us a negative integer?

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It doesn't really make sense
for someone to spend negative 15

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minutes in the shower.

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Let's take a look at the
structure of a while loop.

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For a while loop, as long as the given
condition of the while loop is true,

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then the body of that loop will
continue to execute until that condition

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evaluates to false.

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And then we exit the loop and
we continue along in our code.

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Now, let's take a look at a close
relative of the while loop--

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a do-while loop.

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A do-while loop is unique in that it
executes the body of the loop at least

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once.

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So within the body of the do-while
loop, that thing will happen once,

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and then we'll go to
a regular while loop.

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As long as that condition is
true, we'll repeat that process.

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The do-while loop is particularly useful
when it comes to validating user input.

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That's because we know that we want
to prompt the user at least once.

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So take a look at this snippet of code.

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Here I prompt the user for an
integer asking them for a number.

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Now, I store that number in the integer
n, the variable that I declared above.

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Now, if n is valid, then my
condition will evaluate to false

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and so I can progress
to the rest of my code.

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And I don't need to re prompt them.

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But if they give me an
invalid number, then my loop

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will repeat, prompting
them again and again

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until they give me a valid number.

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When you prompt the user, make sure
that you read the problem specification

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very carefully and use the exact
same string that we ask you for.

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That way your program
will pass check 50.

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OK, now that we've prompted the
user and validated their input,

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we have the minutes that
they spent in the shower.

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From there, let's go on to calculating
the equivalent number of water bottles.

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Now, you might be able
to tell immediately

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how to convert between minutes spent
in the shower to bottles of water used.

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But let's start getting
into the practice

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of detecting these sorts of patterns.

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That way when they get more complicated,
we've already dealt with them.

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So we have one minute
spent in the shower being

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equivalent to 12 bottles of water,
two minutes is equivalent to 24.

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Moving on, we have five minutes
would be 60 bottles of water.

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So for any n minutes spent in the
shower, how many bottles of water

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are used?

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In C, if you'd like to conduct
some arithmetic operations

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then you have addition, subtraction,
multiplication, and division using

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these symbols as shown on the slide.

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All right, so now we know how to convert
between minutes spent in the shower

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and bottles used.

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The last thing to do is
to print that number.

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Say I wanted to print the
fact that I have 0 dogs.

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I would pass in the
string, "I have 0 dogs."

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and you'll notice the /n there just
prints a new line for nice formatting.

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Now, as a dog lover, the fact
that I have 0 dogs is quite sad

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and so I know that that
number is going to change.

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So instead of hard
coding that number n I'm

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going to introduce, a place holder
for an integer in that string.

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So if earlier on in my code
I declared an integer n.

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Then later on in my print statement,
I can print, "I have %i I dogs."

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And then pass in the variable
that I want to be printed--

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in this case n.

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And so when I adopted my dog
Mayu, n incremented by 1.

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And so calling that print statement
would print, "I have 1 dog."

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You've already done so
much work, so let's make

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sure that your code passes check
50 by reading the specification

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carefully so that you know exactly
what to output for those bottles

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so that the string matches
the spec perfectly.

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And with that, you've
completed the problem.

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My name is [? Zamila, ?]
and this was water.

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