How to get the week number (With respect to month).See example in description

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Refer this post

// variable type of in_Today DateTime (this will be your input datetime)
// variable type of Basedate is DateTime
// variable type of week is Int64

Assign Basedate = new DateTime(in_Today.Year, in_Today.Month, 1)
Assign week = DateAndTime.DateDiff(DateInterval.WeekOfYear ,Basedate, in_Today, FirstDayOfWeek.Monday,FirstWeekOfYear.Jan1)
actual value = week+1