Exercise - Write your first code

In this first hands-on exercise, you'll use C# to print a hallowed programmer's phrase to the standard output of a console.

Write your first line of code

There's a long-standing tradition among software developers to print the phrase "Hello World!" to the console output window. As you'll experience, you can learn a lot about programming and the C# programming language from this simple exercise.

Enter code into the C# Code Editor

A C# code editor is available to use directly in the browser: C# Code Editor. This editor provides a lightweight environment for writing, running, and testing C# code without needing to install any software on your local computer.

1. Open the C# Code Editor in a new browser window or tab.

   You can position the browser windows side-by-side so that you can refer to these instructions while you work in the C# Code Editor.

2. Enter this code exactly as it appears into the C# Code Editor:

   Console.WriteLine("Hello World!");
   

   You'll see an explanation of how and why it works soon. But first, you should experience it running, and ensure you entered it correctly. To do that, you'll run your code.

   Note

   You might be tempted to select Copy and Run and skip all the keystrokes. However, there are benefits to typing code yourself. Entering the code yourself reinforces memory and understanding that will help you gain insights that you wouldn't get otherwise.

Run your first code

1. Press the ▶️ Run button

   The Run button performs two tasks:

   • It compiles your code into an executable format that a computer can understand.
   • It runs your compiled application and, when written correctly, will output "Hello World!".

Observe your results

1. In the output console, observe the result of your code. You should get the following output:

   Hello World!
   

What to do if you get an error message

Writing C# code is an exercise in precision. If you type just one character incorrectly, you'll get an error message in the output area when you run the code.

For example, if you were to incorrectly enter a lower-case c in the word console like so:

console.WriteLine("Hello World!");

You'd get the following error message:

Error summary:
  CS0103: The name 'console' does not exist in the current context

What does this error message mean?

C# is a case-sensitive language, meaning that the C# compiler considers the words console and Console as different as the words cat and dog. Sometimes, the error message can be a bit misleading. You'll need to understand the true reason why the error exists, and that comes through learning more about C#'s syntax.

Similarly, if you used single-quotation marks (') to surround the literal string Hello World! like so:

Console.WriteLine('Hello World!');

You would get the following error message:

Error summary:
  CS1012: Too many characters in character literal

You can use the message as a clue as you investigate the problem. But what does the error message mean? What exactly is a "character literal?" Later, you'll learn more about literals of various data types (including character literals). For now, be careful when you're entering code.

Fortunately, errors are never permanent. You merely spot the error, fix it, and rerun your code.

If you got an error when you ran your code, take a moment to look at it closely. Examine each character and make sure you entered this line of code exactly.

Common mistakes new programmers make:

• Entering lower-case letters instead of capitalizing C in Console, or the letters W or L in WriteLine.
• Entering a comma instead of a period between Console and WriteLine.
• Forgetting to use double-quotation marks, or using single-quotation marks to surround the phrase Hello World!.
• Forgetting a semi-colon at the end of the command.

Each of these mistakes prevents your code from compiling successfully.

The code editor highlights pre-compilation errors to help you easily identify and correct mistakes as you develop your code. You can think of it like a spell-checker that helps you fix grammar or spelling errors in a document.

Assuming you were successful in the previous steps, let's continue.

Display a new message

In this task, you'll comment out the previous line of code, then add new lines of code in the .NET Editor to print a new message

1. Modify the code you wrote so that it's prefixed by a code comment using two forward slashes //:

   // Console.WriteLine("Hello World!");
   

   You can create a code comment by prefixing a line of code with two forward slashes //. This prefix instructs the compiler to ignore all the instructions on that line.

   Code comments are helpful when you're not ready to delete the code yet, but you want to ignore it for now. You can also use code comments to add messages to yourself or others who may later read the code, reminding you of what the code is doing.

2. Add new lines of code to match the following code snippet:

   Console.Write("Congratulations!");
   Console.Write(" ");
   Console.Write("You wrote your first lines of code.");
   

3. Press the ▶️ Run button again. This time, you should get the following output.

   Congratulations! You wrote your first lines of code.
   

The difference between Console.Write and Console.WriteLine

The three new lines of code you added demonstrated the difference between the Console.WriteLine() and Console.Write methods.

Console.WriteLine() prints a message to the output console. At the end of the line, it adds a line feed similar to pressing Enter or Return to create a new line.

To print to the output console, but without adding a line feed at the end, you use the second technique, Console.Write(). So, the next call to Console.Write() prints another message to the same line.

Update the message

1. Update your code to match the following code snippet:

   Console.WriteLine("Congratulations!");
   Console.Write("You wrote your first lines of code.");
   

2. Press the ▶️ Run button again. This time, you should get the following output.

   Congratulations!
   You wrote your first lines of code.
   

This code helps demonstrate the difference between the two methods. A new line is appended by Console.WriteLine(), and Console.Write() prints the output on the current line.

Congratulations on writing your first lines of code!