CODEWITHSUNDEEP
c#regexvalidation
user811362
user811362

Reputation: 15

Regex to validate a number for length and start digits

I'm looking for a regex that will validate a number. One part is easy ^(\d{5,9})$ the string representing the number must be 5 to 9 digits.

Part 2 I don't know how: It must NOT start with 9999

How can I add that part?

Upvotes: 0

Views: 314

Answers (3)

John
John

Reputation: 88

I would recommend that you use your programming language's normal string functions to extract the first four characters of the string and compare them to "9999". This will be more efficient than a negative lookahead assertion, and also easier to read.

I suppose there could be some special circumstances where it needs to conform to the regex format. If this is the case, then the other answers have what you need. But I think it's good to realize not everything involving pattern matching has to use a regular expression.

Upvotes: 0

Nicholas Carey
Nicholas Carey

Reputation: 74197

You want a negative-lookahead assertion, anchored at start of string:

Regex rx = new Regex( @"^(?!9999)\d{5,9}$" ) ;

Upvotes: 1

Casimir et Hippolyte
Casimir et Hippolyte

Reputation: 89547

This do the job:

^(?!9999)\d{5,9}$

(?!....) is a negative lookahead and means "not followed by"

Upvotes: 2

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