C# ---- 数据类型(params/ref/out)

  class MainClass
     {
          public void Jiaohuan(int x,int y)
          {
               x=x+y;
               y=x-y;
               x=x-y;
          }
      MainClass mainclass = new MainClass();
      int a = 12;
      int b = 35;
      mainclass.Jiaohuan(a,b);
      Console.WriteLine ("a={0},b={1}",a,b);//然而实参没有交换
      int c =30;
      int d = c;
      d = 40;
      Console.WriteLine ("c={0},d={1}",c,d);

 class MainClass
     {
          public void Jiaohuan( ref int x,ref int y)//ref只适用于值类型，相当于把值类型转化为引用类型
          {
               x=x+y;
               y=x-y;
               x=x-y;
          }
          public static void Main (string[] args)
          {
               MainClass mainclass = new MainClass();
               int a = 12;
               int b = 35;
               mainclass.Jiaohuan(ref a,ref b);
               Console.WriteLine ("a={0},b={1}",a,b); //形参的值发生改变后，实参的值也会发生改变      

   public void Maopao(int[]a)
          {
               for(int i = 0;i<a.Length-1;i++){
                    for(int j =0;j<a.Length-i-1;j++){
                         if(a[j]>a[j+1])
                         {
                              int temp = a[j+1];
                         a[j+1] = a[j];
                         a[j] = temp;
                         }
                    }
               }
  int[] s = {1,5,6,7,2,4,3};
  int[] h = s;
  h[1] = 10;
  Console.WriteLine (s[1]);
  mainclass.Maopao(s);

         int  num = 23;
         object obj = num;
         Console.WriteLine (obj);

         int count = (int)obj;
         Console.WriteLine (count); 

          public void PrintArr( params int[] a)//可变数组参数params
          {
               foreach(int n in a)
               {
                    Console.Write (n+" ");
               }
          }
          
          //输出数组
          int[] sh = {12,54,45,32,45};
          mainclass.PrintArr(sh);
          Console.WriteLine ();
          mainclass.PrintArr(2,5,7,8,4,9);//使用params后可省去定义数组
          Console.WriteLine ();
          mainclass.PrintArr();

          public void PrintArr(int a,int b,params int[] jk)//可变数组参数params与别的值类型同存在
          {
               foreach(int y in jk)
               {
                    Console.Write (y+" ");
               }
          }
          mainclass.PrintArr(2,5,7,8,4,9);//使用params后可省去定义数组

    //买烟的方法  +out
        public int Maiyan(int money,out int change)//把零钱输出来,有out的话是把形参赋值给实参
        {
             int num = money/20;
             change = money%20;
              return num;
         }
 
               //输出参数,当返回值为两个，则在方法定义参数处加out，
               int lingqian;
               int number = mainclass.Maiyan(50,out lingqian);//拿了多少钱
               Console.WriteLine (number);
               Console.WriteLine (lingqian);

// keywords_params.cs
 
using System;
 
class App
{
    public static void UseParams(params object[] list)
    {
        for (int i = 0; i < list.Length; i++)
        {
            Console.WriteLine(list[i]);
        }
    }
 
    static void Main()
    {
        // 一般做法是先构造一个对象数组，然后将此数组作为方法的参数
        object[] arr = new object[3] { 100, ‘a‘, "keywords" };
        UseParams(arr);
 
        // 而使用了params修饰方法参数后，我们可以直接使用一组对象作为参数
        // 当然这组参数需要符合调用的方法对参数的要求
        UseParams(100, ‘a‘, "keywords");
 
        Console.Read();
    }
}