c#输入两个正整数：年份和月份,以空格分隔，输出这一年的这一月有多少天。需要考虑闰年。用switch

在C#中，你可以使用`switch`语句结合`DateTime`类来处理这个问题。首先，我们需要获取给定年份和月份对应的天数，同时考虑到闰年的情况。以下是一个示例代码：

using System;

class Program
{
    static void Main(string[] args)
    {
        Console.Write("请输入年份(yyyy) 和 月份:mm：");
        string input = Console.ReadLine(); // 获取用户输入
        string[] numbers = input.Split(' '); // 分割字符串

        int year = Int32.Parse(numbers[0]); // 年份
        int month = Int32.Parse(numbers[1]); // 月份

        int daysInMonth;
        switch (month)
        {
            case 1:
                daysInMonth = 31; break; // January always has 31 days
            case 2:
                if (IsLeapYear(year)) // 判断是否为闰年
                    daysInMonth = 29;
                else
                    daysInMonth = 28;
                break;
            case 3:
                daysInMonth = 31; break; // March has 31 days
            case 4:
                daysInMonth = 30; break; // April has 30 days
            case 5:
                daysInMonth = 31; break; // May has 31 days
            case 6:
                daysInMonth = 30; break; // June has 30 days
            case 7:
                daysInMonth = 31; break; // July has 31 days
            case 8:
                daysInMonth = 31; break; // August has 31 days
            case 9:
                daysInMonth = 30; break; // September has 30 days
            case 10:
                daysInMonth = 31; break; // October has 31 days
            case 11:
                daysInMonth = 30; break; // November has 30 days
            case 12:
                daysInMonth = 31; break; // December has 31 days
            default:
                throw new ArgumentException("Invalid month"); // 处理无效月份
        }

        Console.WriteLine($"{year}年{month}月有 {daysInMonth} 天。");

        // 判断闰年的辅助函数
        bool IsLeapYear(int year)
        {
            return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
        }
    }
}

当你运行这个程序并输入年份和月份时，它会计算出指定月份的天数，并考虑闰年的情况。