C#学习（二）

这周主要学习了一些基础知识，大部分都和C++、JAVA很像，来看看吧。

1. 简单的变量。变量如何被赋值、静态变量不能被赋值、简单的for循环、while循环、do-while循环，都与C++、JAVA等十分相似。

下面是简单的变量赋值、静态变量如何不能被赋值、简单的if语句和switch语句。

··········································································变量赋值···············································································

·······································································静态变量不能被赋值····································································

·······················································if语句··········································································

 ·····································································switch语句········································································· 

2. 显示转换。一般情况下，值域大的变量不能赋值给值域小的变量，但是可以通过显示的转换进行这项操作。

short x;
int y = 500;
//赋值语句: 值域小的变量 = 值域大的变量；
x = y ; // does not compile 
x =(short) y; //cast, explicit conversion OK

但是我们要保证赋给x的值不能超过它能表示的最大值。

3. 特殊的goto语句

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Week2
{
    class Program
    {
        static void Main(string[] args)
        {
            int testme = 2;
            switch (testme)
            {
                case 2:
                    testme = 5;
                    Console.WriteLine("testme = " + testme);
                    goto case 3;    //执行case 3
                case 3:
                    testme = 1;
                    Console.WriteLine("testme = " + testme);
                    break;
                default:
                    testme = 2;
                    Console.WriteLine("testme = " + testme);
                    break;
            }
        }

    }
}

执行结果：

这说明执行完case 2又执行了case3.

4. 对象和类。

新建类，定义它的成员变量和方法。如果没有构造函数，编译器会自动生成一个无参数的构造函数。没有访问修饰符的成员会被定义成私有。C#共有5种访问修饰符：

下面是自定义的Time类（没有定义有实际作用的方法，这里只是练习一下创建并使用类）：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Week2
{
    class Time
    {
        // private variables: 没有访问修饰符的成员为私有类型
        int Year; 
        int Month; 
        int Date;
        int Hour; 
        int Minute; 
        int Second;

        // public methods: explicitly(显式)定义为 public
        public void DisplayCurrentTime()
        {
            Console.WriteLine("stub for DisplayCurrentTime");
        }

    }
}

定义类对象并调用类方法：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Week2
{
    class Program
    {
        static void Main(string[] args)
        {
            Time time = new Time();
            time.DisplayCurrentTime();
        }

    }
}

运行结果

调用DisplayCurrentTime()成功。