While working in a project, I got stuck in a issue in which I needed a generic function that converts the date string in any format to a desired date format.

The solution which I got is as follows:

public static string FormatDate(string input, string goalFormat, string[] formats)
        {
            var c = CultureInfo.CurrentCulture;
            var s = DateTimeStyles.None;

            var result = default(DateTime);

            if (DateTime.TryParseExact(input, formats, c, s, out result))
                return result.ToString(goalFormat);

            throw new FormatException("Unhandled input format: " + input);
        }

This is a generic method which will accept date string in any format and will convert it into the desired format.

Example of Usage:

var formats = new[] { "dd/MM/yy", "dd/MM/yyyy", "MM/dd/yy", "yyyy/MM/dd", "MM/dd/yyyy" };
            string d = "27/06/2015";
            string t = ClassName.FormatDate(d, "MM/dd/yyyy", formats);

  The parameters you have to pass is the input string,Desired format,formats array(That will contain all the possible formats of the input date string).

Note:-> The format of the input string passed should must be mentioned inside the formats array.