namespace SJ_random
{
    class Class_main
    {
        static void Main()
        {
            Class_random rdm = new Class_random();

            Random rm = new Random();

            string s = string.Empty;                //置空字符串.

            Console.WriteLine(rdm.random_1(s, rm)); //調用方法 random_1 ，產生隨機數.

            Console.Write(rdm.random_2(s, rm));     //調用方法 random_2 ，產生隨機數.

            Console.ReadKey();
        }
    }

    public class Class_random
    {
        /// <summary>
        /// 方法一，生成隨機數。
        /// </summary>
        /// <param name="s">接收生成的隨機數</param>
        /// <param name="rm">random的實例</param>
        /// <returns>生成的隨機數</returns>
        public string random_1(string s, Random rm)
        {
            for (int i = 0; i < 4; i++)
            {
                int k = rm.Next();

                char j = (char)('0' + (char)(k % 10));

                s += j.ToString();
            }
            return s;
        }

        /// <summary>
        /// 方法二，生成隨機數。
        /// </summary>
        /// <param name="s">接收生成的隨機數</param>
        /// <param name="rm">random的實例</param>
        /// <returns>生成的隨機數</returns>
        public string random_2(string s, Random rm)
        {
            s = Convert.ToString(rm.Next(1000, 9999));

            return s;
        }
    }
}