CODEWITHSUNDEEP
regex
fractal5
fractal5

Reputation: 2132

Regexp - optional dot in a decimal number

I've written two Regexp's that allow for the following formats:

Where Y can be 1 or 2 digits. And X is unlimited.

Regex1: ^\d+(?:\.{0,1})(?:\d{1,2})?$

Regex2: ^\d+\.{0,1}(?:\d{1,2})?$

Is one better than the other?

Is there a better way to write this?

Also, why doesn't this one work where the dot is just set as optional: ^\d+(?:\.)(?:\d{1,2})?$

Thanks.

Upvotes: 5

Views: 9166

Answers (2)

Mark Adelsberger
Mark Adelsberger

Reputation: 45659

The reason ^\d+(?:\.)(?:\d{1,2})?$ doesn't work is that it does not make the . optional as you say. the (?: ... ) is not how you make something optional; its main use is grouping multiple things together (so that a subsequent ?, '+', etc. could modify the group) without producing a capture value.

Make something optional by following it with a ?. So:

^\d+\.?(?:\d{1,2})?$

should work. It's simpler - so imo preferable - to either of the other options you showed. Simpler still:

^\d+\.?\d{0,2}$

ought to be fine.

Upvotes: 7

anubhava
anubhava

Reputation: 785038

Is there a better way to write this?

You can use this regex without any groups:

^\d+\.?\d{0,2}$

RegEx Demo

\d{0,2} allows for absence of any digits after period. Also note that \.{0,1} is same as \.?

Upvotes: 5

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