程序代码：

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            double sum = 0;
            for (int i = 1; i <= 100; i++)
            {
                sum += (1.0 / i);
            }
            Console.WriteLine("1/1 + 1/2 + 1/3 + 1/4 + ... + 1/100 = " + sum);

            int s = 0;
            int x = 1;
            for (int i = 1; i <= 10000; i += x)
            {
                x += 2;
                s += i;
            }
            Console.WriteLine("1 + 4 + 9 + 16 + ... + 10000 = " + s);

            sum = 0;
            x = 1;
            for (int i = 0; i < 100; i++)
            {
                sum += (4.0 / x);
                x += 2;
            }
            Console.WriteLine("4/1 + 4/3 + 4/5 + 4/7 + ... 前100项之和 = " + sum);
            Console.Read();
        }
    }
}

程序代码：

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            double sum = 0;
            for (int i = 1; i <= 100; i++)
            {
                sum += (1.0 / i);
            }
            Console.WriteLine("1/1 + 1/2 + 1/3 + 1/4 + ... + 1/100 = " + sum);

            int s = 0;
            int x = 1;
            for (int i = 1; i <= 10000; i += x)
            {
                x += 2;
                s += i;
            }
            Console.WriteLine("1 + 4 + 9 + 16 + ... + 10000 = " + s);

            sum = 0;
            x = 1;
            for (int i = 1; i <= 100; i++)
            {
                if (i % 2 == 0)
                {
                    sum -= (4.0 / x);
                }
                else
                {
                    sum += (4.0 / x);
                }
                x += 2;
            }
            Console.WriteLine("4/1 - 4/3 + 4/5 - 4/7 + ... 前100项之和 = " + sum);
            Console.Read();
        }
    }
}