Using RegExpressions to validate GPA

This is the shortest expression:

/^[0-4]\.\d\d$/

Explanation:

^     - Start of line
[0-4] - One digit in the range 0-4
\.    - A dot, which needs to be escaped with a backslash.
        Without the backslash it means "any character apart from line break"
\d\d  - Two digits (any value from 0-9)
$     - End of line

Try like this:

/^[0-4]\.\d{2}$/