1   class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5           //num1,num2,必须赋值
 6             int num1 = 10;
 7             int num2 = 5;
 8             Exchage(ref num1,ref num2);//调用方法，必须在变量前，必须加ref关键字
 9         
10         }
11   /// <summary>
12         /// 使用ref方法,参数必须加ref关键字
13         /// </summary>
14         /// <param name="num1"></param>
15         /// <param name="num2"></param>
16         private static void Exchage(ref int num1,ref int num2)
17         {
18             //交换前
19                 Console.WriteLine("num1的值：{0}；num2的值：{1}", num1, num2);
20                 int temp = num1;
21                 num1 = num2;
22                 num2 = temp;
23                 //交换后
24                 Console.WriteLine("num1的值：{0}；num2的值：{1}", num1, num2);
25                 Console.ReadKey();
26         }

 1    class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5         int sum;//不需赋值，即使赋值，也会被覆盖
 6             NumSum(10,5,out sum);
 7             Console.Write(sum);
 8             Console.ReadKey();
 9         }
10    /// <summary>
11         /// 求和
12         /// </summary>
13         /// <param name="num1"></param>
14         /// <param name="num2"></param>
15         /// <param name="sum"></param>
16         private static void NumSum(int num1,int num2,out int sum)
17         {
18             sum = num1 + num2;
19 
20         }
21 }