C # BASICS (6) (enumeration, array, namespace)

I,Enumeration.

Enumeration is user-definedInteger type. When declaring an enumeration type, you must specify a group of acceptable instance values that can be included in the enumeration.

Let's look at an example.

  

 Code 

   Using  System;
  Using  System. windows;
  Namespace  Gosoa.com.cn
{
  Class  Myfirstclass
{
 Static     Void  Main ()
{
  Int  Useraage  =  (  Int  ) User. fatherage;
Console. writeline (useraage );
}

  Public     Enum  User
{
Age  = 18  ,  //  Age  
  Gread  =  2  ,  //  Grade  
  Fatherage  =  65     //  Father's age 
  }
}
}
 

 

In the example 65. Public Enum user Is to declare User . Age, gread, fatherage Is its three options. Three specific values are assigned respectively. Int useraage = (INT) user. fatherage; This defines Useraage And assign the value User. fatherage , That is 65.

Let's take a look at a small example.

 
Code


   Static VoidMain ()
{
User usertemp=User. gread;
Console. writeline (usertemp. tostring ());
}
 

 

in this example, the output is gread String. Why? Because enumeration is instantiated in the background as derived from system. enum structure, which indicates that you can call methods and perform some operations on them. The example above is a description.

II,Array.

First, declare an integer array.Int [] usercount;

Int []This indicates an integer array,UsercountIs the array name.

Let's look at another declaration method:Int [] usercount = new int [20];

This example declares20.

Note,All arrays are of reference type..

Array, we will briefly introduce this point here, and we will learn the array together with the set later.

III,Namespace.

Let's look at an example.

  

 Code 

   Using  System;
  Namespace  Gosoa.com.cn
{
  Public     Class  Myfirstclass
{
  Public    String  Geturl ()
{
  Return    "  Gosoa.com.cn  "  ;
}

  Static     Void  Main ()
{
Www.gosoa.com.cn. myfirstclass urlclassnew  =  New  Www.gosoa.com.cn. myfirstclass ();
  String  URL  = Urlclassnew. geturl ();
Myfirstclass myfirstclassnew  =  New  Myfirstclass ();
  String  Url2  =  Myfirstclassnew. geturl ();
Console. writeline (URL );
Console. writeline (url2 );
}
}
}

  Namespace  Www.gosoa.com.cn
{
  Public     Class Myfirstclass
{
  Public     String  Geturl ()
{
  Return     "  Www.gosoa.com.cn  "  ;
}
}
}
 

 

In this example, there are two Namespace . Note: Two Namespace The class names in are the same and all have Geturl () Method. But in the first Class Main () When we call these two methods, no error is reported, because the two classes are located in two different namespaces, thus avoiding the conflict of class names.

The output result is Www.gosoa.com.cn AndGosoa.com.cn

In this example, Gosoa. myfirstclass urlclassnew = new gosoa. myfirstclass (); Is used to instantiate Gosoa. myfirstclass This class. We need to use the struct class. Namespace + "." + Class Name In this way.

If the namespace name is very long, it will be very long, so we can useUsingStatement is simplified.

we can see that, the first sentence before each class is always using system; This is because all C # many classes are included in System namespace.

You can also create an alias for the namespace. For example, in the previous example, we can use

Using gosoa = www.gosoa.com.cn; To introduce Namespace.