regex for integer or floating point number with two decimals

Question

I want to validate my currency field with regex. I want to allow the following pattern entries

1.23
1
.45
0.56
56.00

No comma should be allowed. I've tried d+(.dd) but it allows only first, fourth and fifth entries. d+(?:.dd+)? allows all but third one.

Answer 1

Use d* instead of d+ before the decimal to match zero or more digits. Also add anchors (^ and $) or else it will pass as long as there is any match available. This would also validate an empty string, so if necessary you can use a lookahead to make sure there is at least one digit:

^(?=.*d)d*(?:.dd)?$