Check if a string has a certain length and contains certain letters

Question

So I want to check that a string has all these attributes:

Five characters long, and
The first character is one of:
- O, or
- S, or
- J, or
- C, and
The last four characters are digits.

This is my code:

Console.Write("IDnumber : ");
IDnumber= Console.ReadLine();
IDnumberLength = IDnumber.Length;
if (MemberNumber.Length == 5  && 
    char.IsLetter(IDnumber[0]) &&  <-- I know how to validate any letter but not certain letter
    char.IsDigit(IDnumber[1]) && 
    char.IsDigit(IDnumber[2]) &&
    char.IsDigit(IDnumber[3]) &&
    char.IsDigit(IDnumber[4]))

Sounds like the regular expression [OSJC][0-9]{4} would fit. Alternatively, your code plus new char[] { 'O', 'S', 'J', 'C' }.Contains(IDnumber[0]). — CodeCaster
– CodeCaster, Commented Nov 27, 2016 at 0:33
just keep in mind that the char.Is methods also check for Unicode characters fileformat.info/info/unicode/category/Nd/list.htm, so IDnumber[1] >= '0' && IDnumber[1] <= '9' might be preferred — Slai
– Slai, Commented Nov 27, 2016 at 0:53

Enigmativity · Accepted Answer · 2016-11-27 03:02:19Z

4

You could use Regex like this:

var regex = new Regex("^[OSJC][0-9]{4}$");

Console.WriteLine(regex.IsMatch("J1234"));
Console.WriteLine(regex.IsMatch("J124"));
Console.WriteLine(regex.IsMatch("X1234"));

That would give you:

True
False
False

In your code you could use it like this:

Console.Write("IDnumber : ");
IDnumber = Console.ReadLine();
if (Regex.IsMatch(IDnumber, "^[OSJC][0-9]{4}$"))
{
    // Success
}
else
{
    // Failed
}

edited Nov 27, 2016 at 3:02

answered Nov 27, 2016 at 0:45

Enigmativity

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1 Comment

Joel Coehoorn Over a year ago

I'd add anchors for the front and back. This regex also matches 1O1234x.

Dai · Accepted Answer · 2016-11-27 00:37:18Z

0

Without using a regular-expressions:

Boolean isValid =
    value.Length == 5 &&
    ( value[0] == 'O' || value[0] == 'S' || value[0] == 'J' || value[0] == 'C' ) &&
    Char.IsDigit( value[1] ) &&
    Char.IsDigit( value[2] ) &&
    Char.IsDigit( value[3] ) &&
    Char.IsDigit( value[4] );

answered Nov 27, 2016 at 0:37

Dai

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