題目： 有100塊錢要買100只雞 其中 公雞 5元一隻 母雞 3元一隻 小雞 一元3只 有幾種買雞的方法？

用for迴圈

int add = 0;
            for (int j = 0; j <= 20; j++)    //公雞
            {

                for (int k = 0; k <= 33; k++)   // 母雞
                {
                    for (int l = 0; l <= 300; l++)    //小雞
                    {
                        if (15 * j + 9 * k + l == 300 && j + k + l == 100)  
                        {
                            add++;
                        }
                    }
                }
            }
            Console.WriteLine("共有" + add + "種買法");

結果：

用while迴圈做

            int x = 0, y, z;
            while (x <= 20)
            {
                y = 0;
                while (y <= 33)
                {
                    z = 100 - x - y;
                    if (15 * x + 9 * y + z == 300)
                    {
                        Console.WriteLine("公雞" + x + "只，母雞" + y + "只，小雞" + z + "只");
                    }
                    y++;
                }
                x++;
            }

結果：