Csharp 简明教程

C

在我们学习 C# 编程语言的基础构建模块之前，让我们看一下最低限度的 C# 程序结构，以便我们可以在后续的章节中将其作为参考。

Before we study basic building blocks of the C# programming language, let us look at a bare minimum C# program structure so that we can take it as a reference in upcoming chapters.

Creating Hello World Program

C# 程序包含以下部分 −

A C# program consists of the following parts −

  1. Namespace declaration

  2. A class

  3. Class methods

  4. Class attributes

  5. A Main method

  6. Statements and Expressions

  7. Comments

让我们看一下输出“Hello World”的简单代码 −

Let us look at a simple code that prints the words "Hello World" −

using System;

namespace HelloWorldApplication {
   class HelloWorld {
      static void Main(string[] args) {
         /* my first program in C# */
         Console.WriteLine("Hello World");
         Console.ReadKey();
      }
   }
}

编译并执行此代码后，会产生以下结果 −

When this code is compiled and executed, it produces the following result −

Hello World

让我们看一下给定程序的不同部分 −

Let us look at the various parts of the given program −

  1. The first line of the program using System; - the using keyword is used to include the System * namespace in the program. A program generally has multiple *using statements.

  2. The next line has the namespace declaration. A namespace is a collection of classes. The HelloWorldApplication namespace contains the class HelloWorld.

  3. The next line has a class declaration, the class HelloWorld contains the data and method definitions that your program uses. Classes generally contain multiple methods. Methods define the behavior of the class. However, the HelloWorld class has only one method * Main*.

  4. The next line defines the Main method, which is the entry point for all C# programs. The *Main * method states what the class does when executed.

  5. The next line /…​/ is ignored by the compiler and it is put to add * comments* in the program.

  6. The Main method specifies its behavior with the statement Console.WriteLine("Hello World"); WriteLine is a method of the Console class defined in the System namespace. This statement causes the message "Hello, World!" to be displayed on the screen.

  7. The last line Console.ReadKey(); is for the VS.NET Users. This makes the program wait for a key press and it prevents the screen from running and closing quickly when the program is launched from Visual Studio .NET.

请注意以下几点：

It is worth to note the following points −

  1. C# is case sensitive.

  2. All statements and expression must end with a semicolon (;).

  3. The program execution starts at the Main method.

  4. Unlike Java, program file name could be different from the class name.

Compiling and Executing the Program

如果您使用 Visual Studio.Net 来编译和执行 C# 程序，请执行以下步骤：

If you are using Visual Studio.Net for compiling and executing C# programs, take the following steps −

  1. Start Visual Studio.

  2. On the menu bar, choose File → New → Project.

  3. Choose Visual C# from templates, and then choose Windows.

  4. Choose Console Application.

  5. Specify a name for your project and click OK button.

  6. This creates a new project in Solution Explorer.

  7. Write code in the Code Editor.

  8. Click the Run button or press F5 key to execute the project. A Command Prompt window appears that contains the line Hello World.

您可以通过使用命令行（而不是 Visual Studio IDE）来编译 C# 程序：

You can compile a C# program by using the command-line instead of the Visual Studio IDE −

  1. Open a text editor and add the above-mentioned code.

  2. Save the file as helloworld.cs

  3. Open the command prompt tool and go to the directory where you saved the file.

  4. Type csc helloworld.cs and press enter to compile your code.

  5. If there are no errors in your code, the command prompt takes you to the next line and generates helloworld.exe executable file.

  6. Type helloworld to execute your program.

  7. You can see the output Hello World printed on the screen.