help with Regex - need up to 3 number after the dot (.)

Question

I need help with a regex matching a number. I need up to 3 digits after the dot (.):

12345    ok
12       ok
12.1     ok
12.12    ok
12.123   ok
12.1234  Error
1.123456 Error

how to do it? Thanks in advance.

Answer 1

^\d+(\.\d{1,3})?$

Answer 2

regex.match(@"\d+\.\d{,3}"};

Answer 3

You can try:

^\d+|(\d+\.\d{1,3})$

• \d - Single digit
• \d+ - one or more digits, that is a number.
• \. - dot is a metachar..so to match a literal dot, you'll need to escape it.
• {1,3} - between 1 to 3 (both inclusive) repetitions of the previous thing.
• ^ and $ - Anchors so that we match entire thing not just part of something.

Answer 4

\d+(?:\.\d{1,3})?

Explanation:

\d+        # multiple digits
(?:        # start non-capturing group  
  \.       # a dot
  \d{1,3}  # 1-3 digits
)?         # end non-capturing group, made optional

Answer 5

Are you sure you need regex to solve the problem you are having? How about:

bool ContainsAtMostThreeNumbersAfterDot(string str)
{
  int dotIndex = str.IndexOf(".");
  float f;
  return float.TryParse(str, out f) && str.Length - dotIndex < 3;
}

This code is nor complete or 100% correct (take is just as an idea and handle the specific cases yourself), but IMHO, it expresses the intent a lot more clearly than using a regex to solve a problem that does not need regex at all.