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C# Syntax


In the previous chapter, we created a C# file called Program.cs, and we used the following code to print "Hello World" to the screen:


using System;

namespace HelloWorld
  class Program
    static void Main(string[] args)
      Console.WriteLine("Hello World!");    


Hello World!

来试试吧 »

Example explained

Line 1: using System means that we can use classes from the System namespace.

Line 2: A blank line. C# ignores white space. However, multiple lines makes the code more readable.

Line 3: namespace is a used to organize your code, and it is a container for classes and other namespaces.

Line 4: The curly braces {} marks the beginning and the end of a block of code.

Line 5: class is a container for data and methods, which brings functionality to your program. Every line of code that runs in C# must be inside a class. In our example, we named the class Program.

Don't worry if you don't understand how using System, namespace and class works. Just think of it as something that (almost) always appears in your program, and that you will learn more about them in a later chapter.

Line 7: Another thing that always appear in a C# program, is the Main method. Any code inside its curly brackets {} will be executed. You don't have to understand the keywords before and after Main. You will get to know them bit by bit while reading this tutorial.

Line 9: Console is a class of the System namespace, which has a WriteLine() method that is used to output/print text. In our example it will output "Hello World!".

If you omit the using System line, you would have to write System.Console.WriteLine() to print/output text.

Note: Every C# statement ends with a semicolon ;.

Note: C# is case-sensitive: "MyClass" and "myclass" has different meaning.

Note: Unlike Java, the name of the C# file does not have to match the class name, but they often do (for better organization). When saving the file, save it using a proper name and add ".cs" to the end of the filename. To run the example above on your computer, make sure that C# is properly installed: Go to the Get Started Chapter for how to install C#. The output should be:

Hello World!

WriteLine or Write

The most common method to output something in C# is WriteLine(), but you can also use Write().

The difference is that WriteLine() prints the output on a new line each time, while Write() prints on the same line (note that you should remember to add spaces when needed, for better readability):


Console.WriteLine("Hello World!");  
Console.WriteLine("I will print on a new line.");

Console.Write("Hello World! ");
Console.Write("I will print on the same line.");  


Hello World!
I will print on a new line.
Hello World! I will print on the same line.

来试试吧 »

In this tutorial, we will only use WriteLine() as it makes it easier to read the output of code.

C# 练习

Test Yourself With 练习


Insert the missing part of the code below to output "Hello World!".

static void (string[] args)
  .("Hello World!");    

Start the Exercise

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