In this lecture, we're continuing our discussion of the selection control
structure. Here are the module learning objectives
for the module. Last time, we talked about the different
variations of the if statement we could use to make
decisions in our program. This time, we're going to look at another
C# statement we can use to implement the selection control
structure in C#. And that statement is called the switch
statement. So, now you should go do an in-lecture
quiz to see if you paid attention to my
previous sentence. I have already built a project that
demonstrates the switch statement. Although it doesn't really do any of the
demonstration stuff yet, if I Ctrl+F5, do you want the shiny
thing? Yes, no, h, whatever, press any key. So, this is exactly as before, this is
exactly as before. This is the part that we're going to do
slightly differently. So the new statement we're looking at is
the switch statement. And the way the switch statement works is we type the word switch, which is a
keyword. And then in parenthesis we put the name of
the variable or an expression if we choose to.
That we want to switch on basically, that we want to evaluate its value and
take appropriate action. So, before we had answer as a key portion
of our Boolean expressions. And it turns that answer is exactly the
variable that we want to switch on here. The syntax is a little different, well maybe a lot different from the if
statement. So for the different values that the
answer variable can have, we add cases.
So we have case, lower case y. I'm going to compare this to i, and I'm
going to print that message that we used before, that I probably won't remember verbatim, but we'll remember it
close enough. You have the shiny thing. Now, it feels like we should be all the
way done here, but we're not quite, because as you can see,
we're getting an error message. And that error message says we can't fall
through from this case to other cases. Other programming languages let you do
that. And sometimes that's really useful, and
other times it leads to horrible bugs that take hours and hours
to find. So C# doesn't let us do it. So at the end of every case we do, we're
going to type the word, break. When we do that, that compilation error
goes away. And now, we have a form that will behave exactly like our first if statement worked
last time. When I Ctrl+F5, if I say lower case yes, I
have the shiny thing. If I say h, nothing.
And sadly, if I say upper case Y, I still get nothing.
So it turns out, that we can list multiple
cases, multiple values for the answer variable in this
particular case that will do this stuff here.
And so, if I just stack these values like this, then I can
check both answer being lower case y and the answer being
upper case y. And it will do this in both cases.
Let's check it to see. Lower case y still works the way we
expected. Now upper case Y also gives us the shiny
thing. And finally, we'll check that h, nothing.
So, we can do the same thing for no.
Where we don't have the shiny thing. And I pressed F5 by mistake so it flashes
right away. Let's try that again. Lower case n, don't have the shiny thing.
Upper case n, don't have the shiny thing. Still showing you that y works in both
cases. And, of course, h still doesn't give us
anything. Now just to, so this sort of works in a similar way to the if, else if, else
thing. Where it figures out which of these things
matches, if you will, and does the appropriate stuff inside. I'll point out that I cannot down here
decide, oh I want to do another thing with lower case y, because that has
already been included. We've already used that value in a case,
so we can't use it again. You might wonder though, how we can go
about doing that your a noob message. Because we sure don't want to have to say,
case a, case, upper case A, case b, all of the other possible
characters that are not y or n. What we really want is something that corresponds to the else in our if
statement. And luckily, we get such a thing in the
switch statement. We type the word default. Which really means, if none of these other
things match, then do this instead. And here's where we can do our new
message. And, we're still going to have to add a
break, because we add a break at the end of every clause we include in a
switch statement. And now, when I Ctrl+F5, I'll still check
y. I'll still check n.
And I'll try h where I get my new message. So, you might wonder why we care?
If we already have this if else, if else structure, why
would we want a switch statement instead? And it turns out that I covered it here
because it's sort of the other statement we use for
selection in C#. We find it to be most useful in our game
development when we're using something called an
enumeration. An enumeration is basically a data type
that has specific values. Don't worry. We'll look at enumerations and see how
they all work so, so no worries that we haven't talked
about it yet. But we'll discover that when we're using
an enumeration, we find that switch statements tend to seem a little
more intuitive as we implement them. I'm going to have you, if you do the
optional lab, I'm going to have you do some practice with both if statements and
switch statements, because they're both useful
tools for selection. And you'll pick the most appropriate one
as you continue on with your programming. So next time, we will start talking what,
we've talked about two different C# statements.
Next time we'll show using selection in actual game situations.