class Program
    {
        static double h = 100;      //两地总距离
        static double s = 0;        //小鸟飞行总距离 
        const int birdSpeed = 30;   //小鸟飞行速度
        const int aSpeed = 20;      //火车速度A
        const int bSpeed = 15;      //火车速度B

        static void Main(string[] args)
        {
            for (; ; )
            {
                double time = h / (birdSpeed + aSpeed);     //第一次小鸟与火车相遇所用时间
                h = h - aSpeed * time + bSpeed * time;      //相遇后两火车之间距离
                if (h < 0.1)                                //判断是否相遇
                {
                    Console.WriteLine(s);
                    break;
                }
                else
                {
                    s = s + birdSpeed * time;               //没有相遇,累计小鸟飞行距离
                    time = h / (birdSpeed + bSpeed);        //飞向另一火车所用时间
                    h = h - aSpeed * time + bSpeed * time;  //剩余距离
                    if (h < 0.1)
                    {
                        Console.WriteLine(s);
                        break;
                    }
                    else s = s + birdSpeed * time;
                }
            }
            Console.ReadKey();
        }
    }

得出的总飞行距离不对. 可能是思路不对吧 . 刚才学不久别笑我啊