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[MUSIC]

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Our program always
charges users $2 per can.

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It takes the number of cans
the user wants to order, and

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multiplies it by 2 to get the total cost.

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Our last requirement is to provide
a discount for large orders of can.

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Specifically, if the order is for
100 cans or more,

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the price should be $1.50 per can.

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If it's for 50 cans or more,
the price should be $1.75 per can, and

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all other orders should be the full price,
$2 per can.

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Our first problem here is to figure
out which discount we should apply.

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Are they ordering 100 cans or more?

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50 to 99?

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Less than 50?

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To do this, we're going to
need a way to compare numbers.

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This code will be a little too
complicated to embed within a string.

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So first, let's move the part that
calculates the price out to a method.

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We'll add a price function that takes
the number of cans being ordered, and

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a parameter named quantity.

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Notice that we're having our function
return a double floating point value,

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not an int.

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An integer return value
would work right now,

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because we're only returning
whole dollar amounts.

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But when we add discounts later,
we'll be using fractional dollar amounts,

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like $1.75 or $1.50 per can.

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So we'll prepare for

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this by setting the price function up with
a double floating point return type now.

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Quantity times 2 is actually an int value,
but

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int is a less precise type, and
double is a more precise type.

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So the conversion from int to double
will be performed implicitly.

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Now that we've set the price method up, we
can make a call to it in the main method.

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We pass it the number of cans and store
its return value in a new total variable.

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Then we update our call to
Console.WriteLine to use the new

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total variable, instead of embedding the
calculation in the interpolated string.

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Also, I just noticed that we're still
using our entry variable to print

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the number of cans the user entered.

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While that has worked so

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far because the string is going to contain
the same content as the number variable,

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it seems safer to use the same variable
that we're passing to the price function.

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So I'm gonna go ahead and
change that from entry to number.

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So let me save this, and confirm
that it still works in the same way.

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I'll make an order of 100 cans,
and our total is $200.

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But this time the total was
calculated by the price method.

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Now that we've moved our price
calculation out to a separate method,

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we can work towards applying
a discount for large orders.

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In order to know which discount to apply,
we need to be able to tell if the order

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quantity is over 100, if it's between
50 and 100, or if it's below 50.

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C# uses comparison operators to
tell whether one value is equal to,

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greater than, or less than another.

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Comparison operators
return a Boolean Value.

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Boolean Values are either true or false.

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They're represented in C# code
by the words true and false.

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Note, that these are not strings, so
they're not surrounded by quotes.

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The most commonly used
comparison operators in C#,

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are the greater than operator, the less
than operator and the equality operator.

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The greater than operator will return
true if the value to its left is

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greater than the value to its right.

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The less than operator will return true
if the value to its left is less than

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the value to its right.

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And the equality operator will return
true if the value to its left and

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the value to its right are equal.

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Let me save this and try running it so
you can see the results.

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So we assign the value 75
to the quantity variable.

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And then we test whether
quantity is greater than 50,

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which gives us a result of true.

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We test whether quantity is less than 50,

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which of course gives us a result
of false, because quantity is 75.

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And then we test whether quantity
is equal to 75, which it is.

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Now I want to warn you about something,

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it's very important not to confuse the
quality operator, which is a double equal

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sign, with the assignment operator
which is a single equals sign.

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So for example,
this right here is a simple check

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whether quantity is equal to 99, it makes
no change to the quantity variable.

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Let me save this and
try running it to show you.

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You can see that first we compare
quantity to 99 to see if they're equal.

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And then we print the value in quantity,
and we can see that quantity is still 75.

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This will not be the case if we
confuse the assignment operator and

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the quality operator.

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This code here doesn't check
whether quantity is equal to 99.

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It reassigns the value 99 to quantity.

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Let me save that and
show you what happens.

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So you can see that the check for
a equality doesn't change the value in

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quantity, but
the accidental reassignment does.

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Quantity is now set to 99
at the end of this program,

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which may not be what you wanted to do.

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It's very important not to
confuse the assignment and

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the equality comparison operators.

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Let me get rid of this code here.

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And now let's talk about the greater
than or equal and less than or

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equal to operators.

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The greater then or
equal to operator returns true

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if the value to its left is greater
than or equal to the value to its right.

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The less than or equal to operator returns
true if the value to its left is less than

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or equal to the value to its right.

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So since quantity is set to 75 now,

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this will return true because
75 is greater than 50.

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And this will return false because 75
is neither less than or equal to 50.

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However, if we were then to reset
the quantity variable to 50,

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both of these operations will be true
because quantity isn't greater than 50 but

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it is equal to it.

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And quantity isn't less than 50,
but again, it's still equal to it.

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Let me save this and run it so
you can see the results.

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And you can see that both of
these last operations are true.

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The last operator I wanna show
you is the inequality operator

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written with an exclamation
point followed by an equal sign.

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The exclamation point can
be read aloud as not.

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So != can be read aloud as not equal.

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It's the opposite of
the equality operator.

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So since quantity is set to 50, quantity
not equal 50 will actually be false.

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This is the opposite of quantity
equals 50, which is going to be true.

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Let me save this and show you the result.

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Quantity not equal to 50 gives us false,
because quantity is equal to 50.

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By the way, you should never
compare a string to a numeric type,

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you'll get an error.

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So here we have two string values, and

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we're attempting to compare them to
two numeric values, to integers.

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Let me save this and show you the result.

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And we get compile errors for
both those lines.

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You should only do a comparison if you
can convert one class to match the other.

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So if we were to do an int.Parse
conversion on each of

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these strings, this will work.

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Because now both of these comparisons
are comparing one integer to another.

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By the way, all the comparison operators
we just showed you work in pretty much

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every programming language out there.

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So remember them,
because you'll be using them a lot.