C # obtain the first and last days of a month

/// <Summary>
/// Obtain the first day of a month
/// </Summary>
/// <Param name = "datetime"> obtain the first day of the month </param>
/// <Returns> </returns>
Private datetime firstdayofmonth (datetime)
{
Return datetime. adddays (1-datetime. Day );
}

//// <Summary>
/// Obtain the last day of a month
/// </Summary>
/// <Param name = "datetime"> obtain the time of the last day of the month. </param>
/// <Returns> </returns>
Private datetime lastdayofmonth (datetime)
{
Return datetime. adddays (1-datetime. Day). addmonths (1). adddays (-1 );
}

//// <Summary>
/// Obtain the first day of last month
/// </Summary>
/// <Param name = "datetime"> obtain the current time of the first day of the last month. </param>
/// <Returns> </returns>
Private datetime firstdayofpreviousmonth (datetime)
{
Return datetime. adddays (1-datetime. Day). addmonths (-1 );
}

//// <Summary>
/// Obtain the last day of the previous month
/// </Summary>
/// <Param name = "datetime"> obtain the current time of the last day of the last month. </param>
/// <Returns> </returns>
Private datetime lastdayofprdviusmonth (datetime)
{
Return datetime. adddays (1-datetime. Day). adddays (-1 );
}