Methods

Before we could even start on the cat food store program, we had to spend the first stage learning about variables, types, and namespaces. But now we're ready to actually begin work on the store.

Cat Food Store Features

• Display welcome message
• Ask for quantity
• Calculate total
• Discount for large orders

The first requirement is to display a welcome message to the user. Let's work on that now.

• If you click the "Launch Workspace" button on this video's page, it will start a workspace with a new C# project.
• There are a few files here, but there's really only on we care about: the Program.cs file.
• C# source code is stored in plain text files, but instead of .txt, the file name usually ends in .cs.
• If we click the file to open it, we'll see that it's set up and ready for us to write code.

Program.cs:

class Program
{
    static void Main(string[] args)
    {

    }
}

• We need to add our code between the two curly braces following this static void Main line here. We'll be talking about what this static void Main line means in just a moment.
• We need to print a welcome message for the user.
• But as we showed in the previous stage, we don't want to have to type the System namespace all over our code.
  • So here at the top of the file, let's use a using directive for the System namespace: using System;
  • And then we can delete the System namespace before Console.WriteLine.
• We can try running this by going to the console area and typing: dotnet run
  • The .NET framework will find our Program.cs file, compile it, and execute the code it contains.
  • And there in the terminal we'll see the string we specified.

So we were able to print a welcome message by calling the Console.WriteLine method. We've talked about methods briefly in the first stage, but we never really explained what they are. It's time to do that now.

• When we called GetType() on various values to see what their type was, that was a method: 42.GetType();
• When we called ToUpper() on a string to capitalize it, that was a method: "hi".ToUpper();
• And we are actually writing code for a new method right now. This static void Main code here defines a new method, a special one that gets called when our program starts.
• A method is a group of code statements that are put together to perform a particular task.
• WriteLine is a method. The task it carries out is to write a line of text out to the console.
  • You run a method by calling it.
  • To call a method, type its name, followed by a pair of parentheses: Console.WriteLine()
• When calling a method, you can provide arguments inside the parentheses. Arguments are values associated with a method call that change what the method does when it runs.
  • Let's write the string "Hello" here within the parentheses, so it's passed as an argument to the method: "Hello"
  • Most methods have a specific number and type of arguments they expect.
  • Some methods expect no arguments. Others expect two, three, or more.
• And of course, every statement in C# needs to end with a semicolon, so let's add one here at the end of the line: ;
• Let's try a different method call: System.Threading.Thread.Sleep();
  • This method causes the program to wait for a certain amount of time before continuing.
  • How does the Sleep method know how long it should wait? We can pass the duration in as an argument to the method call.
  • It takes an integer with the number of milliseconds (or thousandths of a second) it should wait for.
  • So 1000 milliseconds would cause it to sleep for 1 second.
  • We type the argument here between the parentheses: 1000.
• Let's also add another call to WriteLine, so we can tell when the program is done sleeping: Console.WriteLine("done sleeping");
• dotnet run
• Let's try changing the argument to Sleep so that it pauses longer. I'll change it to 3000 milliseconds so it sleeps for 3 seconds: 3000
• dotnet run
• A quick issue with the Sleep method that I want to address before we move on.
  • You'll notice that System.Threading.Threads.Sleep appears to start with the System namespace.
  • Since we have a using System; directive at the top of the file, you might think we can remove System. from the front of the method name.
  • But let's try to run this: dotnet run
  • We get an error: "The name 'Threading' does not exist in the current context".
  • The problem is that System.Threading is a separate namespace from System. So we can't just remove System from the front of the method name.
  • Let me undo that change.
  • Instead, we need to also add a using System.Threading; directive at the top of the file: using System.Threading;
  • Note that we're not replacing the using System; directive, we're writing this directive in addition.
  • Now that we have a using System.Threading; directive, we can remove not System, but System.Threading from the front of the method name.
  • dotnet run

So now you know - whenever we've been typing a name followed by a pair of parentheses, we've been calling methods. Up next, we'll show you how to define your own methods.