1、函数输入参数对于函数而言，相当于已经赋值了的变量，直接可用。输出参数相当于定义了一个变量，需要在函数中为其赋值，然后调用函数的时候将所赋值带出函数。例1：输入a,b,c的值，判断是不是一个一元二次方程：class Program    {        public string fangcheng(double a, double b, double c, out double x1, out double x2)        {            double d = b * b - 4 * a * c;            if (a == 0)            {                          x1 = -b/c;                x2 = -b/c;                return "不是一元二次方程";            }            else             {                     if (d < 0)                {                                    x1 = -1;                    x2 = -1;                    return "无解";                }                else if (d == 0)                {                                       x1 = -(b + Math.Sqrt(d)) / (2 * a);                    x2 = -(b - Math.Sqrt(d)) / (2 * a);                    return "有两个相等的实数根";                }                else                 {                                      x1 = -(b + d) / (2 * a);                    x2 = -(b - d) / (2 * a);                    return "有两个不相等的实数根";                }            }        }        static void Main(string[] args)        {            Program aaa = new Program();            Console.WriteLine("请输入a的值：");            double a = int.Parse(Console.ReadLine());            Console.WriteLine("请输入b的值：");            double b = int.Parse(Console.ReadLine());            Console.WriteLine("请输入c的值：");            double c = int.Parse(Console.ReadLine());            double x1, x2;            Console.WriteLine(aaa.fangcheng(a,b,c,out x1,out x2));            Console.WriteLine("x1=" + x1 +"\n"+ "x2=" + x2);            Console.ReadLine();        }}2、递归例2：（1）猴子摘桃子，后一天摘前一天的一半加一个，第七天还有一个，总共有几个？（2）一人赶着一群羊，到一个村就卖掉1/3加一只，到第七个村庄时还有2只，总共有几只？（3）一对幼兔两个月长成成兔并生下一对幼兔，9个月后有几对？class Program    {        public int taozi(int day)        {            if (day == 7)            {                return 1;            }            else            {                int n = 2 * (taozi(day + 1) + 1);                return n;            }        }        public int yang(int cun)        {            if (cun == 7)            {                return 2;            }            else            {                int n = 3 * (yang(cun + 1) + 1);                return n;            }        }        public int tuzi(int yue)        {            if (yue == 0)            {                return 1;            }            else            {                int n = tuzi(yue-2)*2;                return n;            }        }        static void Main(string[] args)        {            Program dd = new Program();            Console.WriteLine(dd.taozi(1));            Console.WriteLine(dd.yang(1));            Console.WriteLine(dd.tuzi(9));            Console.ReadLine();        }}