Question

New to regex syntax here. Trying to write a regex to provide some input validation.

What I need is a regex to match a whole number, or a decimal with exactly one digit past the decimal.

Good Match
1
12
100
1.1
100.1
1.0

No Match
1.22
1.
0
012

Here is what I came up with but it doesn’t work:

Regex.IsMatch(paidHours, "\\d+[.]?[0-9]?")

Answer 1

Edited answer after OP question edit.

Regex.IsMatch(paidHours, @"^[1-9][0-9]*(\.[0-9])?$");

Explanation:

^      : Start of the String
[1-9]  : A single number between 1 and 9
[0-9]* : Zero or more number(s) between 0 and 9 
         ([0-9]? would match zero or one number and the String "100" would not match the regex)
(      : Start of a group
\.     : A point
[0-9]  : A single number between 0 and 9
)?     : End of the group. The group must be repeated zero or one time
$      : End of the String

Please note that \d is not exactly equivalent to [0-9]: \d matches any unicode digit. For instance, this character ௮ will be matched if you use \d but won’t be if you use [0-9].