.Net_用控制台程序打印指定行数的三角型（面试题）

 static void Main(string[] args)
        {

            while (true)
            {

                int k = 1;
                Console.WriteLine("请输入行数");
                int num = Convert.ToInt32(Console.ReadLine());
                while (num < 3 || num > 21)
                {
                    
                    Console.WriteLine("输入错误，请从新输入行数");
                    num = Convert.ToInt32(Console.ReadLine());
                }
                int num2 = num;
                for (int i = num; i > 0; i--)
                {
                    if (num2 == i)
                    {
                        for (int j = 0; j < i*2 - 1; j++)
                        {
                            Console.Write("*");

                        }
                        Console.Write("\r\n");
                    }
                    else
                    {
                        for (int j = 0; j < k; j++)
                        {
                            Console.Write(" ");
                        }
                        k++;
                        for (int d = 0; d < i*2 - 1; d++)
                        {
                            Console.Write("*");

                        }
                        Console.Write("\r\n");
                    }

                }
            }

            Console.ReadKey();
        }