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Asked: 2026-05-27T16:19:05+00:00

I need a Regular Expression allowing user to input numbers, plus, minus and parentheses.

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I need a Regular Expression allowing user to input numbers, plus, minus and parentheses.

User can only input:

  • At most one open parenthesis ‘(‘.
  • At most one close parenthesis ‘)’.
  • At most one plus ‘+’
  • As many minus ‘-‘ but not after each other.
  • Exactly 11 numbers.

Here are valid inputs:

(0)+12-3-4-56-7890
+)0(12345-678-90
+01234567890
+(01234567890)
01234567890
-01-234+5678-90
(01234567890)
)01234567890(

And following are not valid:

0123456--7890
0((1234567890
01234567890))
++01234567890
123456
++123456789

I’m using C# for programming and if it helps order of open and close parentheses can become mandatory too. so )01234567890( will not be valid.

Thanks in advance

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1 Answer

  1. Editorial Team

    This regex passes your examples, but might not be exactly what you’re looking for. It should point you in the right direction.

    ^(?!.*-{2,})(?!(?:.*\)){2,})(?!(?:.*\(){2,})(?!\+{2,})(?:\D*\d\D*){11}$
    • (?!.*-{2,}) Cannot contain two or more hyphens.
    • (?!(?:.*)){2,}) Cannot contain two or more closing parentheses.
    • (?!(?:.*(){2,}) Cannot contain two or more opening parentheses.
    • (?!+{2,}) Cannot start with more than two addition symbols.
    • (?:\D*\d\D*){11} Must contain 11 instances of a numeric character surrounded by anything.

    However, this is very confusing and fairly inefficient. I bet the regex could be rewritten to be much quicker, but won’t be much easier to understand.

    I suggest that you follow MisterJack’s suggestion instead of pursue a regex. It’ll be easier to maintain.

    EDIT

    ^(?!.*--)(?!.*(\(|\)|\+).*\1)(?:\D*\d\D*){11}$

    I’ve consolidated the parentheses and plus symbol rules into one negative lookahead using a backreference. This also restricts the number of parens and pluses to just one of each. I couldn’t get it to restrict to just a certain set of characters, but you might be able to do that in a second pass with another regex.

    • ^ Match from beginning of the string
    • (?!.*–) Do not allow consecutive hyphens
    • (?!.* ((|)|+).*\1) Do not allow two or more instances of () or +
    • (?:\D*\d\D*){11} Must contain 11 digits, allow non-digit characters before and after, such as hyphen.
    • $ Match to end of string

    I tried a negative and positive lookahead to restrict the characters, but couldn’t get it to work right. I also tried to replace \D with [()+-] but that didn’t work either. Maybe someone else will add a comment to show how to restrict the characters. I’d sure love to see how someone else does it in this regex.

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