class Program
    {
        static void Main(string[] args)
        {
            //练习
            diyiti();
            dierti();
            disanti();
            disiti();
            diwuti();
            diliuti();
            diqiti();
         

            //九九乘法表
            for (int i = 1; i <= 9; i++)
            {
                for (int j = i; j <= 9; j++)
                {
                    Console.Write("{0}X{1}={2}\0", i, j, i * j);
                }
                Console.WriteLine();
            }









            //while练习；continue;break；
            int i = 0;
            while (i <= 9)
            {
                i++;
                if (i == 3)
                {

                    continue;//终止本次循环；继续下一个循环
                    // break;//终止整个循环；
                }

                Console.WriteLine("i,{0}", i);


            }


            // do while练习；不管条件是否成立都执行一次；

            int k = 1;
            do
            {
                Console.WriteLine(k);
                k++;

            } while (k < 0);











            //水仙花数
            for (int i = 100; i < 1000; i++)
            {
                int a = i % 10;//个位
                int b = i / 10 % 10;//十位
                int c = i / 100;//百位；
                if (a * a * a + b * b * b + c * c * c == i)
                {
                    Console.WriteLine("水仙花数{0}", i);
                }

            }
            //2/1+3/2+5/3+1...
            double fenzi = 2;
            double fenmu = 1;
            double sum = 0;
            for (int i = 0; i < 20; i++)
            {
                sum += fenzi / fenmu;
                fenzi = fenzi + fenmu;
                fenmu = fenzi - fenmu;
            }
            Console.WriteLine("求和{0}", sum);

            Console.ReadKey();
        }

        static void diyiti()
        {
            //------------第一题----------
            int js = 0;//计数；
            int num = 0;
            for (int i = 1; i < 1000; i++)
            {
                if (i % 7 == 0 || i % 10 == 7 || i / 10 % 10 == 7 || i / 100 == 7)
                {
                    Console.WriteLine("这些数分别是{0}\n\n", i);
                    js++;
                    num += i;
                }

            }

            Console.WriteLine("第一题个数{0}，和{1}\n\n", js, num);


        }

        static void dierti()
        {
            //------------第二题----------
            double num = 0;
            for (double i = 1; i <= 100; i++)
            {
                num += 1 / i;//整形除整形还是整形
            }
            Console.WriteLine("第二题{0}\n\n", num);



        }

        static void disanti()
        {

            //------------第三题----------
            double num = 0;
            for (double i = 1; i <= 98; i++)
            {
                num += i / (i + 1);

            }
            Console.WriteLine("第三题求和：{0}\n\n", num);

        }


        static void disiti()
        {

            //------------第四题----------
            double num = 0;
            for (double i = 0; i < 100; i++)
            {
                num += (i + 1) / (2 * i + 1);

            }
            Console.WriteLine("第三题求和：{0}\n\n", num);
        }



        static void diwuti()
        {
            //------------第五题----------
            Console.WriteLine("请输入4位数");
            string a = Console.ReadLine();
            int c = Convert.ToInt32(a);
            int js = 0;
            for (int i = 2; i < c / 2 + 1; i++)
            {
                if (c % i == 0)
                {
                    js++;
                }
            }
            if (js > 0)
            {
                Console.WriteLine("第五题输入的数：不是素数\n\n");
            }
            else
            {
                Console.WriteLine("第五题输入的数：是素数\n\n");
            }
        }

        static void diliuti()
        {
            //------------第六题----------

            int a = 0;
            int sum = 0;
            for (int i = 0; i < 6; i++)
            {
                a = a * 10 + 4;
                Console.WriteLine(a);
                sum += a;
            }
            Console.WriteLine("第六题求和{0}\n\n", sum);

        }



        static void diqiti()
        {
            //------------第七题----------
            int sum = 0;
            int i = 1;
            int j = 1;
            while (i < 1000)
            {
                sum = 0;
                j = 1;
                while (j < i)
                {
                    if (i % j == 0)
                    {
                        sum += j;
                       // Console.WriteLine(j);
                    }
                    j++;
                }
                if (sum == i)
                {
                    Console.WriteLine(i);
                }
                i++;
            }
        }

      
    }