Question

I have a string that might be between 1 and 8 characters long. I need to convert those into a day, a month and a year. For missing parts I will use the current one.

The code I have now is kind of big and ugly, and I was wondering if someone have a more clever idea on how to do this.

My current code is listed below:

var day = DateTime.Now.Day;
var month = DateTime.Now.Month;
var year = DateTime.Now.Year;

switch (digits.Length)
{
    case 1:
    case 2:
        day = int.Parse(digits.Substring(0));
        break;

    case 3:
    case 4:
        day = int.Parse(digits.Substring(0, 2));
        month = int.Parse(digits.Substring(2));
        break;
    case 5:
    case 6:
    case 7:
    case 8:
        day = int.Parse(digits.Substring(0, 2));
        month = int.Parse(digits.Substring(2, 2));
        year = int.Parse(digits.Substring(4));
        break;
    default:
        break;
}

Note: I know this isn’t taking culture into consideration, but it is not supposed to 🙂

I tried to do it like this:

day = int.Parse(digits.Substring(0, 2));
if(digits.Length > 2)
    month = int.Parse(digits.Substring(2, 2));
if(digits.Length > 4)
    year = int.Parse(digits.Substring(4, 4));

But it will throw an ArgumentOutOfRangeException if the string is 1, 3, 5, 6 or 7 digits long… so that didn’t work so well. If only the Substring method would have just taken as many letters as it could instead of failing when there were not enough letters to “fill” the substring…

Could regular expressions maybe be used for this?

Answer 1

Look at the TryParseExact method.

DateTime date;
if (DateTime.TryParseExact(
    digits, 
    new[] { "dd", "ddMM", "ddMMyyyy" }, 
    CultureInfo.InvariantCulture, 
    DateTimeStyles.None, 
    out date))
{
    int day = date.Day;
    int month = date.Month;
    int year = date.Year;    
}