ref关键字

ref是引用的方式传递参数，参数必须初始化。也就意味传入方法中的不再是形参，而是引用该实参。ref关键字在定义 和 使用时需要在前面添加 ref关键字表示引用，对比代码如下：

ref引用传参 

        //ref:引用的方式传递参数
        public static int findMax(ref int num1, ref int num2)
        //public static int findMax(int num1, int num2)
        {
            num1 *= 2;
            num2 *= 2;
            return num1 + num2;
        }
        private static void Main(string[] args)
        {
            //参数必须初始化不然会报错
            int num1 = 1;
            int num2 = 2;
            int num3 = 0;
            num3 = findMax(ref num1, ref num2);
            //num3 = findMax(num1, num2);
            
            Console.WriteLine($"num1 = {num1}, num2 = {num2}, num3 = {num3}");
                              //num1 = 2, num2 = 4, num3 = 6
            Console.ReadKey();
        }

值传参

        //ref:引用的方式传递参数
        //public static int findMax(ref int num1, ref int num2)
        public static int findMax(int num1, int num2)
        {
            num1 *= 2;
            num2 *= 2;
            return num1 + num2;
        }
        private static void Main(string[] args)
        {
            //参数必须初始化不然会报错
            int num1 = 1;
            int num2 = 2;
            int num3 = 0;
            //num3 = findMax(num1, num2);
            num3 = findMax(num1, num2);
            
            Console.WriteLine($"num1 = {num1}, num2 = {num2}, num3 = {num3}");
                              //num1 = 1, num2 = 2, num3 = 6
            Console.ReadKey();
        }

out关键字

out关键字与ref关键字一样也是引用传递，在使用out修饰的参数，在定义的时候，可以初始化，也可以不初始化，但是，在方法内部必须赋值。

out输出传参 

        public static int result(int num1, int num2, out int num3)
        //public static int result(int num1, int num2, int num3)
        {
            num3 = (num1 + num2) / 2;
            return num3;
        }
        private static void Main(string[] args)
        {
            int num1 = 2;
            int num2 = 4;
            int num3 = 0;
            int avg = 0;
            avg = result(num1, num2, out num3);
            //avg = result(num1, num2, num3);
            Console.WriteLine($"avg = {avg}, num3 = {num3}");   //avg = 3, num3 = 3
            Console.ReadKey();
        }

 值传递

        //public static int result(int num1, int num2, out int num3)
        public static int result(int num1, int num2, int num3)
        {
            num3 = (num1 + num2) / 2;
            return num3;
        }
        private static void Main(string[] args)
        {
            int num1 = 2;
            int num2 = 4;
            int num3 = 0;
            int avg = 0;
            //avg = result(num1, num2, out num3);
            avg = result(num1, num2, num3);
            Console.WriteLine($"avg = {avg}, num3 = {num3}");   //avg = 3, num3 = 0
            Console.ReadKey();
        }