Question

I have 3 textboxes (day, month, year) and I want to check if input is e.g. day has to be from 1 to 31 and so on.

My code is:

If InputDan.Text < "1" Or InputDan > "31" Then Warning.Text = "Not a valid day input." Else Warning.Text = ""

Also I have day and month input limited to 2 characters and year to 4.
It works fine with numbers from 10 to 31 and it properly puts an warning message when input is 0 or 32 and on.

Here’s the problem…

When I put in numbers from 4 to 9 it puts on a warning message, as I figured out later that program considers empty space after one character input as 0.
So if I enter 4 the program will read it as 40, and so on.

Can I solve this problem with converting String input as Int somehow?

Answer 1

You need to parse the numbers to integer before you can compare them, otherwise >"11" will compare them alphabetically and not by their numerical order.

Dim day As Integer
Dim valid As Boolean = Int32.TryParse(InputDan.Text, day)

Now you know if that input was a correct number and you could show a warning if it was not.

I would suggest a different approach to check whether or not the input was a correct day since you must take the number of days in that month into account(also leap years, different calendars etc). So use the current culture’s calendar and look if the number of days is correct for the given month in this way:

Dim daysInMonth = CultureInfo.CurrentCulture.Calendar.GetDaysInMonth(year, month)
If day > daysInMonth OrElse day < 1 Then
    ' show warning '
End If

(assuming you have already checked the year and month part with Int32.TryParse)