你可以通过下面的代码找到任何月份的最后一天:

var now = DateTime.Now;
var startOfMonth = new DateTime(now.Year, now.Month, 1);
var DaysInMonth = DateTime.DaysInMonth(now.Year, now.Month);
var lastDay = new DateTime(now.Year, now.Month, DaysInMonth);

从下个月的第一天减去一天:

DateTime lastDay = new DateTime(MyDate.Year,MyDate.Month+1,1).AddDays(-1);

此外，如果你也需要它在12月工作:

DateTime lastDay = new DateTime(MyDate.Year,MyDate.Month,1).AddMonths(1).AddDays(-1);

你可以通过下面的代码找到任何月份的最后一天:

var now = DateTime.Now;
var startOfMonth = new DateTime(now.Year, now.Month, 1);
var DaysInMonth = DateTime.DaysInMonth(now.Year, now.Month);
var lastDay = new DateTime(now.Year, now.Month, DaysInMonth);

我只想在每个月的最后一天发射代码，就是这么简单……

if (DateTime.UtcNow.AddDays(1).Day != 1)
{
    // Tomorrow is not the first...
    return;
}

你可以通过一行代码找到这个月的最后一天:

int maxdt = (new DateTime(dtfrom.Year, dtfrom.Month, 1).AddMonths(1).AddDays(-1)).Day;

// Use any date you want, for the purpose of this example we use 1980-08-03.
var myDate = new DateTime(1980,8,3);
var lastDayOfMonth = new DateTime(myDate.Year, myDate.Month, DateTime.DaysInMonth(myDate.Year, myDate.Month));