This course is the second course in the specialization about learning how to develop video games using the C# programming language and the Unity game engine on Windows or Mac. Why use C# and Unity instead of some other language and game engine? Well, C# is a really good language for learning how to program and then programming professionally. Also, the Unity game engine is very popular with indie game developers; Unity games were downloaded 16,000,000,000 times in 2016! Finally, C# is one of the programming languages you can use in the Unity environment. This course assumes you have the prerequisite knowledge from the previous course in the specialization. You should make sure you have that knowledge, either by taking that previous course or from personal experience, before tackling this course. The required prerequisite knowledge is listed in the "Who this class is for" section below. Throughout this course you'll continue building your foundational C# and Unity knowledge by exploring more C# and Unity topics and finishing the Unity game you started at the end of the previous course. The material in this and the previous course is essentially our first programming course for Game Design and Development majors at UCCS. Module 1: Learn how we can store lots of data in arrays and lists and use iteration (looping) to repeat actions in your code Module 2: Learn about abstraction and how we can use it to design and implement console application classes Module 3: Learn how we can use abstraction to design and implement Unity classes Module 4: Add text output (like score!) and sound effects to your Unity games Module 5: Complete final peer review “Unity” is a trademark or registered trademark of Unity Technologies or its affiliates in the U.S. and elsewhere. This course is an independent work and is not sponsored by, authorized by, or affiliated with Unity Technologies or its affiliates
While Loops
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En provenance du cours de University of Colorado System
More C# Programming and Unity
88 notes
University of Colorado System
88 notes
Cours 2 sur 5 dans Specialization C# Programming for Unity Game Development
À partir de la leçon
Arrays, Lists, and Iteration
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Dr. Tim "Dr. T" ChamillardAssociate Professor
Computer Science
We spent the last few lectures talking about for loops and for each loops which
we used when we know, when we get to the loop as we're running our code,
how many times we're going to loop.
In this lecture, we'll look at while loops which give us away to iterate or
loop when we don't know how many times we're going to need to loop.
So of course you need to go do an in video quiz.
And now we'll go look at how while loops work in C#.
We'll start with code that doesn't have a while loop at all and
then we'll add a while loop to it.
So all we do is we prompt for and
get a level from the user, and then we print out that level.
So if I run the game, we'll see of course I'm level 110 and
that's great but the problem is that I can also say I'm level 111 and
it says great, and I could be really bat at wow and say it's -1.
So I really ought to do some input validation
to make sure that the player enters a valid level.
Now I will say that we're going to work on the assumption that they're
entering an integer.
So if they decide to answer those questions by saying Bob,
our code is going to blow up and that's just the way its going to be.
In the next course, we'll learn how to do something called exception handling
that will keep our code from blowing up when that happens.
But for now we're just going to make sure that the integer that they provide to us
is in the appropriate range.
So I will add a comment here that says input validation,
And we'll do that with a while loop.
So what I'll do is between these parentheses,
I will put a Boolean expression and you should remember Boolean expressions
from when we learned about if statements in the previous course.
So a Boolean expression evaluates to true or false.
If the Boolean expression between these parentheses evaluates to true,
then we're going to go into the body of the while loop and do whatever it says.
And then we're going to come back again and see if it's still true.
And if it is, then we'll go into the body of the loop again and so on and
we will keep doing the body of the loop until the Boolean expression we
include here evaluates to false at which point we'll drop out of the loop.
So while loops are really useful because we don't have to know
how many times we're going to loop.
We don't know how many times the user is going to provide
invalid input before they finally provide us with valid input.
So it's great to use a while loop because we can keep looping until
the player provide valid input.
So what constitute invalid input for their while level?
Well, there are actually two ranges of numbers that are invalid.
Anything less than one, and anything greater than 110.
So we'll say that while level is less than one,
or level is greater than 110.
If either one of those is true, because that's how or works, is one or
both of them is true means that the total Boolean expression is true.
So if level is less than one, this will be true, and
if level is greater than 110, this will be true.
It's impossible to have both, right?
You can't think of a number that's both less than one and greater than 110.
But if this Boolean expression evaluates to false, it means that
level is in fact between 1 and 110 inclusive.
So this might feel strange to you, the way we're sort of talking about what's
invalid instead of what's valid but really the bottom line is, we need to loop here
while their input is invalid, so that's what we're checking for.
Once we get valid input, we can move on and print the level.
If they've provided invalid input, we should print an error message and
reprompt.
And you can be as mean or as nice as you want with your error message.
I'll be reasonably nice.
Level must be between 1 and 110.
And then I will read in their level again.
I need to make sure I don't actually redeclare the level of variable,
I just want to use it here so I don't want to declare it again,
I just want to use it again.
Now I can Ctrl+F5, and if I say 1,
that's great because it's a valid input, and
I can say 110 and that's a valid input too.
If however I say -1 for example,
it says the level has to be between 1 and 110.
And I'm going to add a blank line here in a minute because it will look
nicer that way.
But I can be a bad input provider as many times as I want and
the while loop is just going to keep going and
I might decide to go topside instead and still it's going to
keep looping until I enter a level that is valid between 1 and 110.
So I'm going to add that blank line I said I'd add.
And it's always a good idea to retry the code and so
I'll say 0 and that's bad, so I'll say 1 and I'm all done.
With while loops, it's possible for
us to end up in something called an infinite loop.
And you should go do an in video quiz about that.
So of course, we can't actually loop infinitely in our programs because at some
point the sun will burn out or
will rage-throw our computer against the wall or something.
But the big idea is in infinite loop is a loops that loops far more
many times than you had intended when you wrote that particular loop.
There's actually and acronym that we can use to help us avoid infinite loops and
other problems in our while loops and
you should take an in video quiz to guess that.
And the correct answer is, ITM, means initialize, test and modify.
And we should do those three things properly to
implement our while loops correctly.
So let's go back to the code and look at that a little bit.
Not initializing level, so violating the i
part of the acronym is sort of unreasonable in this scenario.
You wouldn't really expect anyone to say this.
int level and then just forgetting to do this piece.
That is pretty unlikely and it won't actually lead to an infinite loop.
And in fact the compiler won't let us do it.
So we will in fact have to give level a value before we can use it here.
So let's restore our code to its former beauty.
And of course we can compile again.
The next thing, the t in that acronym, then test.
What if we got confused about or verses and we did this instead?
So here is the problem.
When I run my code, I might provide an invalid input and it doesn't work anymore.
Because when I enter -1, this piece is true but
-1 is not greater than 110 so
the whole Boolean expression evaluates to false and we just skip the loop entirely.
So that also didn't lead to an infinite loop but
it did lead to misbehavior from the loop.
The last part of the acronym was modify, so if in fact you forgot
to modify the loop control variable, watch what happens.
I'll enter 0, and then I
have an infinite loop with no possibility of actually providing more input.
And the reason for that is this Boolean expression was true, so
I went into the loop and I didn't change level, so
when I come back here again it's true again of course so
I do the loop body and continue and continues and do that.
The input validation example.
It's pretty rare to forget to modify the loop control variable because you're
re-prompting for the input that you're trying to validate.
But there are certainly lots of other situations where forgetting about i,
t, or m, or getting them wrong
will actually lead to while loops that don't behave the way you hope they will.
To recap, in this lecture we learned how to
use while loops when we don't know how many times we're going to need to iterate.
And we also learned the danger of infinite loops in while loops and
how we can help avoid improper while loop behavior
by remembering to initialize, test, and modify correctly.
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