Month Number From Full Month Name
If we need Month Number From Full Month Name then use below code
string monthName = "April";
int monthNumber = DateTime.ParseExact(monthName, "MMMM", CultureInfo.CurrentCulture).Month;
Month Number From Month Abbreviations
If we need to convert a month number from a month abbreviations then use below code
string monthName = "Apr";
int monthNumber = DateTime.ParseExact(monthName, "MMM", CultureInfo.CurrentCulture).Month;