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[MUSIC]

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Before we could even start on
the cat food store program,

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we had to spend the first stage learning
about variables, types and name spaces.

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But now we're ready to actually
begin work on the store.

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The first requirement is to display
a welcome message to the user.

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Let's work on that now.

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If you click the launch workspace
button on this video's page,

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it will start a workspace
with a new C# project.

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There are a few files here but
there's really only one we care about.

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The Program.cs file.

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C# source code is stored
in plain text files, but

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instead of .txt,
the file name usually ends in .cs.

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If we click the file to open it,
we'll see that it's set up and ready for

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us to write code.

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We need to add our code between the two
curly braces following this static

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void Main line here.

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We need to print a welcome message for
the user.

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Previously we were able to
display text on the terminal with

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the System.Console.WriteLine method.

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Let's try that here.

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System.Console.WriteLline.

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Welcome to the cat food store.

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But as we showed in the previous stage,

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we don't wanna have to type the system
namespace all over our code.

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So here at the top of the file let's add a
using directive for the system namespace.

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Using system, and
make sure they end up with a semicolon.

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And then we can delete the system
name space before Console.WriteLine.

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We can try running this by going to
the console area and typing dotnet run.

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The dotnet framework will find our
Program.cs file, compile it and

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execute the code it contains.

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And there in the terminal,
we'll see the string we specified.

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Our program is displaying
a welcome message to the user.

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We can cross the first
requirement off our list.

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So we were able to print a welcome message
by calling the Console.WriteLine method.

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We've talked about methods
briefly in the first stage, but

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we never really explained what they are.

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It's time to do that now.

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When we called GetType on various
values to see what their type was,

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that was a method.

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When we called ToUpper on a string
to capitalize it, that was a method.

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And we're actually writing code for
a new method right now.

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This static void Main code
here defines a new method,

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a special one that gets called
when our program starts.

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A method is a group of code
statements that are put together

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to perform a particular task.

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WriteLine is a method.

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The task it carries out is to write
a line of text out to the console.

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You run a method by calling it.

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To call a method, type its name,
followed by a pair of parentheses.

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When calling a method, you can provide
arguments inside the parentheses.

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Arguments are values associated
with the method call that

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change what the method does when it runs.

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Let's write the string Hello
here within the parentheses, so

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its path is an argument to the method.

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Most methods have a specific number and
type of arguments they expect.

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Some methods expect no arguments.

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Some expect two, three, or more.

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And of course, every statement in C#
needs to end with a semicolon, so

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let's add one here at the end of the line.

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Let's try running this.

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I'll put it back down in
the console to activate it, and

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hit the up arrow to bring
up my previous command.

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And you can see that in addition to
our original call to Console.WriteLine

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which prints welcome
to the cat food store.

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Our second call to Console.WriteLine
runs as well and prints Hello.

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Let's try a different method call.

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System.Threading.Thread.Sleep.

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This method causes the program to wait for

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a certain amount of
time before continuing.

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How does the sleep method
know how long it should wait?

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We can pass the duration in as
an argument to the method call.

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It takes an integer with a number of
milliseconds, or thousandths of a second,

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that it should wait for.

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So 1,000 milliseconds would cause
it to sleep for one second.

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We type the argument here
between the parentheses.

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Let’s also add another
call to WriteLine so

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we can tell when the program
is done sleeping.

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Let me save this and
click down in the console to activate it.

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And let’s try running it, I hit the up
arrow to bring up the previous command and

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hit Enter to run dotnet run.

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And you can see it prints welcome to the
cat food store, pauses for a moment and

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then prints done sleeping.

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Let me try that one more
time to show you again.

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Welcome to the cat food store,
pause, and done sleeping.

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Let's try changing the argument to
sleep so that it pauses longer.

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I'll change it to 3000 milliseconds so
that it pauses for 3 seconds.

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Let me save this.

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Click down on the console, run it again.

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And you can see it pauses for
3 seconds this time.

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A quick issue with the sleep method that
I want to address before we move on.

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You'll notice that
System.Threading.Thread.Sleep

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appears to start with
the System namespace.

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Since we have a using System directive
at the top of the file, you might

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think that we can remove System.dot from
the front of the method method Main.

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But let's try to run this.

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Let me save it, click down in the console,
and say dotnet run.

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We get an error, the name threading
does not exist in the current context.

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The problem is that system.threading
is a separate namespace from system, so

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we can't just remove system from
the front of the method Main.

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Let me undo that change.

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Click my Edit menu and choose undo,

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or there will be a shortcut for
your system, a keyboard shortcut.

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You might want to remember that and
use that instead next time.

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Instead, we need to also add
a using System.Threading

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directive at the top of the file.

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Note that we're not replacing
the using System directive.

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We're writing this directive in addition.

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Now that we have a using System.Threading
directive, we can remove not System,

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but System.Threading from the front
of the call to Thread.Sleep.

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Let me save this, and
click down on the console.

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I'll hit Ctrl L to clear it.

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And I'll hit the up arrow to bring up
my previous command and run dotnet run.

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And our code works as before but
now it's a bit shorter.

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So now you know, whenever we been
typing a name followed by parentheses,

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we've been calling methods.

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Up next, we'll show you how
to define your own methods.