Regex to check if a number is even

Question

Can we have a regex to detect if a number is even ?

I was wondering if we can have a regex to do this instead of usual % or bit operations.

Thanks for replies :)

Answer 1

You can try:

^-?\d*[02468]$

Explanation:

• ^ : Start anchor.
• -? : Optional negative sign.
• \d* : Zero or more digits.
• [02468] : Char class to match a 0 or 2 or 4 or 6 or 8
• $ : End anchor

Answer 2

Sure, you just check if the last number is a 0/2/4/6/8

Answer 3

Try this, I'm not sure if it's the same syntax in java:

^\d*(2|4|6|8|0)$

Answer 4

If it is a string, just check if endsWith(0) || endsWith(2) || .. returns true. If it is number, it is very simple.

Answer 5

Since the correct answer has already been given, I'll argue that regex would not be my first choice for this.

• if the number fits the long range, use %
• if it does not, you can use BigInteger.remainder(..), but perhaps checking whether the last char represents an even digit would be more efficient.

Answer 6

Never use regex for a job that can be easily done otherwise.

I came across this Microsoft blog that says the same: http://blogs.msdn.com/b/bclteam/archive/2005/02/21/377575.aspx