class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                int a, b; int s = 0;
                Console.WriteLine("请输入第一个数：");
                a = Convert.ToInt32(Console.ReadLine());  //最简单的循环数，从a到b的和
                Console.WriteLine("请输入第二个数：");
                b = Convert.ToInt32(Console.ReadLine());
                for (int i = a; i <= b; i++)   //从a一直加到b
                {
                    s = s + i;
                }
                Console.WriteLine("那么从"+a+"到"+b+"的和为"+s);

Console.ReadLine();