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Return Values
4:47Some methods return the result of their work as a return value.
Let's take another look at
the on map method we just wrote.
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The result of these condition checks
is stored in the inBounds variable.
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Then the value stored in
the inBounds variable is returned.
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So if point is found to be inside
the boundaries of the map,
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then the inBounds variable will be true.
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And the value true will be returned
from this method to the caller.
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Otherwise, if the point was found to
be outside the boundaries of the map,
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this method will return false.
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I should mention that we can
actually shorten this code a bit and
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avoid using the inBounds
variable entirely.
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The way we can do this is to return
the result of this expression right away.
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Instead of first storing it in
a variable and then returning it.
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We can type return right here instead and
delete the other return statement.
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See how that works?
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There's now one less variable in our code.
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Also stringing a bunch of
operations together like this
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can quickly make the code
difficult to understand.
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We can alleviate some of this by splitting
the code up into multiple lines like so.
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I can even indent it to line
up with the line above it.
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This is possible to do
because the semicolon
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marks the end of the statement of code.
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So I can put this statement on
as many lines as I want and
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C# still knows to treat
it as a single statement.
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Deciding if and when to split statements
into multiple lines really just
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depends on what you think makes the code
more readable and clearer to the reader.
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I decided to put operations that
deal with the width on one line and
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the height on the other line.
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Indenting so that things line
up vertically can also help.
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All right, we've completed this method.
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Let's go back to the main method in
the game class to try out our new method.
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Don't forget to save the map.cs file.
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We can delete this line and declare a new
point that should be inside our map.
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Our map is eight units wide and
five units high.
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So let's create a point
that's in square 4, 2.
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Now let's call our on map method to
determine if this point is on the map and
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assign the value returned to a variable.
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So I'll say bool isOnMap = map.OnMap and
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then pass it to point.
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Just for fun, let's call OnMap with
a point that we know isn't on the map.
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Just to make sure that we
get the right answer back.
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I'll overwrite the point variable
we just created with the new point.
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I don't have to declare
the variable again because it's
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already declared as a point up here.
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I just want to assign it a new value.
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The same goes for the isOnMap variable.
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I intentionally chose to
make a point in square 8,
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5 in order to illustrate
a common programming mistake.
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At first glance, one might think
that this point is on the map.
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Because the map has a width of eight and
a height of five.
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However, in programming,
by convention we start counting from zero.
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This means that the point on the bottom
left corner of the map is 0, 0.
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And the rightmost point has an x
value of one less than the width.
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The topmost point has a y value
of one less than the height.
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This is called zero base counting.
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This throws a lot of people off.
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Occasionally even experienced
programmers get bitten
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by what's called an off by one error.
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Let's print out the value of
isOnMap to the Console so
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we can see the result of calling OnMap.
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I'll add the system namespace up here and
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then we'll use Console.WriteLine
to print the value of isOnMap.
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So type Console.WriteLine Is OnMap.
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Copy that and do it again down here.
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All right, when we run this
we should see the word true
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followed by the word false
printed to the Console.
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Let's open the Console and
compile and run this code.
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Looks good.
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When we come back we'll learn more
interesting things about methods.
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