闰年算法

/// <summary>
/// 返回月份拥有的天数
/// </summary>
/// <param name="month"></param>
/// <param name="year"></param>
/// <returns></returns>
public static int GetLastDay(int month, int year)
{

    switch (month)
    {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12:
            return 31;
        case 2:
            return year % 100 != 0 && year % 4 == 0 || year % 400 == 0 ? 29 : 28;
        case 4:
        case 6:
        case 9:
        case 11:
            return 30;
    }
    return -1;
}