c#ref与out的区别

class PRogram    {        static void Main(string[] args)        {          //num1,num2,必须赋值            int num1 = 10;            int num2 = 5;            Exchage(ref num1,ref num2);//调用方法，必须在变量前，必须加ref关键字                }  /// <summary>        /// 使用ref方法,参数必须加ref关键字        /// </summary>        /// <param name="num1"></param>        /// <param name="num2"></param>        private static void Exchage(ref int num1,ref int num2)        {            //交换前                Console.WriteLine("num1的值：{0}；num2的值：{1}", num1, num2);                int temp = num1;                num1 = num2;                num2 = temp;                //交换后                Console.WriteLine("num1的值：{0}；num2的值：{1}", num1, num2);                Console.ReadKey();        }

class Program    {        static void Main(string[] args)        {        int sum;//不需赋值，即使赋值，也会被覆盖            NumSum(10,5,out sum);            Console.Write(sum);            Console.ReadKey();        }   /// <summary>        /// 求和        /// </summary>        /// <param name="num1"></param>        /// <param name="num2"></param>        /// <param name="sum"></param>        private static void NumSum(int num1,int num2,out int sum)        {            sum = num1 + num2;        }}