Tutorial: Explore the C# language

This tutorial teaches you C#. You write your first C# program and see the results of compiling and running your code. It contains a series of lessons that begin with a "Hello World" program. These lessons teach you the fundamentals of the C# language.

In this tutorial, you:

Prerequisites

You must have one of the following options:

• A GitHub account to use GitHub Codespaces. If you don't already have one, you can create a free account at GitHub.com.
• A computer with the following tools installed:
  • The .NET 10 SDK.
  • Visual Studio Code.
  • The C# DevKit.

Open Codespaces

To start a GitHub Codespace with the tutorial environment, open a browser window to the tutorial codespace repository. Select the green Code button, and the Codespaces tab. Then select the + sign to create a new Codespace using this environment.

Run your first program

1. When your codespace loads, create a new file in the tutorials folder named hello-world.cs.

2. Open your new file.

3. Type or copy the following code into hello-world.cs:

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

4. In the integrated terminal window, make the tutorials folder the current folder, and run your program:

   cd tutorials
   dotnet hello-world.cs
   

You ran your first C# program. It's a simple program that prints the message "Hello World!" It uses the Console.WriteLine method to print that message. Console is a type that represents the console window. WriteLine is a method of the Console type that prints a line of text to that text console.

Let's move on and explore more. The rest of this lesson explores working with the string type, which represents text in C#. Like the Console type, the string type has methods. The string methods work with text.

Declare and use variables

Your first program prints the string "Hello World!" on the screen.

Your first program is limited to printing one message. You can write more useful programs by using variables. A variable is a symbol you can use to run the same code with different values. Let's try it!

1. Start with the following code:

   string aFriend = "Bill";
   Console.WriteLine(aFriend);
   

   The first line declares a variable, aFriend, and assigns it a value, "Bill". The second line prints the name.

2. You can assign different values to any variable you declare. You can change the name to one of your friends. Add these two lines following the code you already added. Make sure you keep the declaration of the aFriend variable and its initial assignment.

   Important

   Don't delete the declaration of aFriend.

3. Add the following code at the end of the preceding code:

   aFriend = "Maira";
   Console.WriteLine(aFriend);
   

   Notice that the same line of code prints two different messages, based on the value stored in the aFriend variable. You might notice that the word "Hello" is missing in the last two messages. Let's fix that now.

4. Modify the lines that print the message to the following code:

   Console.WriteLine("Hello " + aFriend);
   

5. Run the app again by using dotnet hello-world.cs to see the results.

   You've been using + to build strings from variables and constant strings. There's a better way. You can place a variable between { and } characters to tell C# to replace that text with the value of the variable. This process is called String interpolation.

6. If you add a $ before the opening quote of the string, you can then include variables, like aFriend, inside the string between curly braces. Give it a try:

   Console.WriteLine($"Hello {aFriend}");
   

7. Run the app again by using dotnet hello-world.cs to see the results. Instead of "Hello {aFriend}", the message should be "Hello Maira".

Work with strings

Your last edit was your first look at what you can do with strings. Let's explore more.

You're not limited to a single variable between the curly braces.

1. Try the following code at the bottom of your app:

   string firstFriend = "Maria";
   string secondFriend = "Sage";
   Console.WriteLine($"My friends are {firstFriend} and {secondFriend}");
   

   Strings are more than a collection of letters. You can find the length of a string by using Length. Length is a property of a string and it returns the number of characters in that string.

2. Add the following code at the bottom of your app:

   Console.WriteLine($"The name {firstFriend} has {firstFriend.Length} letters.");
   Console.WriteLine($"The name {secondFriend} has {secondFriend.Length} letters.");
   

You've been using a method, Console.WriteLine, to print messages. A method is a block of code that implements some action. It has a name, so you can access it.

Remove whitespace from strings

Suppose your strings have leading or trailing spaces that you don't want to display. You want to trim the spaces from the strings. The Trim method and related methods TrimStart and TrimEnd do that work. You can use those methods to remove leading and trailing spaces.

1. Try the following code:

   string greeting = "      Hello World!       ";
   Console.WriteLine($"[{greeting}]");
   
   string trimmedGreeting = greeting.TrimStart();
   Console.WriteLine($"[{trimmedGreeting}]");
   
   trimmedGreeting = greeting.TrimEnd();
   Console.WriteLine($"[{trimmedGreeting}]");
   
   trimmedGreeting = greeting.Trim();
   Console.WriteLine($"[{trimmedGreeting}]");
   

The square brackets [ and ] help you visualize what the Trim, TrimStart, and TrimEnd methods do. The brackets show where whitespace starts and ends.

This sample reinforces a couple of important concepts for working with strings. The methods that manipulate strings return new string objects rather than making modifications in place. You can see that each call to any of the Trim methods returns a new string but doesn't change the original message.

Search and replace text in strings

You can use other methods to work with a string. For example, you might use a search and replace command in an editor or word processor. The Replace method does something similar in a string. It searches for a substring and replaces it with different text. The Replace method takes two parameters. These parameters are the strings between the parentheses. The first string is the text to search for. The second string is the text to replace it with. Try it for yourself.

1. Add this code. Type it in to see the hints as you start typing .Re after the sayHello variable:

   string sayHello = "Hello World!";
   Console.WriteLine(sayHello);
   sayHello = sayHello.Replace("Hello", "Greetings");
   Console.WriteLine(sayHello);
   

   Two other useful methods make a string all caps or all lowercase. Try the following code.

2. Type it in to see how IntelliSense provides hints as you start to type To:

   Console.WriteLine(sayHello.ToUpper());
   Console.WriteLine(sayHello.ToLower());
   

   The other part of a search and replace operation is to find text in a string. You can use the Contains method for searching. It tells you if a string contains a substring inside it.

3. Try the following code to explore Contains:

   string songLyrics = "You say goodbye, and I say hello";
   Console.WriteLine(songLyrics.Contains("goodbye"));
   Console.WriteLine(songLyrics.Contains("greetings"));
   

   The Contains method returns a boolean value which tells you if the string you were searching for was found. A boolean stores either a true or a false value. When displayed as text output, they're capitalized: True and False, respectively. You learn more about boolean values in a later lesson.

Challenge

Two similar methods, StartsWith and EndsWith, also search for substrings in a string. These methods find a substring at the beginning or the end of the string. Try to modify the previous sample to use StartsWith and EndsWith instead of Contains. Search for "You" or "goodbye" at the beginning of a string. Search for "hello" or "goodbye" at the end of a string.

You should get true for starting with "You" and ending with "hello" and false for starting with or ending with "goodbye".

Did you come up with something like the following code (expand to see the answer):

string songLyrics = "You say goodbye, and I say hello";
Console.WriteLine(songLyrics.StartsWith("You"));
Console.WriteLine(songLyrics.StartsWith("goodbye"));

Console.WriteLine(songLyrics.EndsWith("hello"));
Console.WriteLine(songLyrics.EndsWith("goodbye"));

For further reading on the string type:

• C# programming guide article on strings.
• How to tips on working with strings.

Cleanup resources

GitHub automatically deletes your Codespace after 30 days of inactivity. If you plan to explore more tutorials in this series, you can leave your Codespace provisioned. If you're ready to visit the .NET site to download the .NET SDK, you can delete your Codespace. To delete your Codespace, open a browser window and navigate to your Codespaces. You should see a list of your codespaces in the window. Select the three dots (...) in the entry for the learn tutorial codespace and select "delete".

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