Question

I am trying to validate a text box and I want the user to only enter between 0.1 and 4.0 and i am using the following regex

^[0-4](\.[0-9]+)?$

the Thing is that is is even accepting 4.1 and so on until 4.9

Any ideas please on how I can fix this

Thanks

Answer 1

Try this

^(?:[0-3](?:\.[0-9]+)?|4(?:\.0)?)$

EDIT

I added non capturing groups.

And as CyprUS asked, here an explanation:
I limited the original regex to go up to 3.9 and added another condition for 4(.0)

NODE                     EXPLANATION
  ^                        //the beginning of the string
  (?:                      //group, but do not capture:
    [0-3]                  //any character of: '0' to '3'
    (?:                    //group, but do not capture (optional):
      \.                   //'.'
      [0-9]+               //any character of: '0' to '9' (1 or more times)
    )?                     //end of grouping
   |                       //OR
    4                      //'4'
    (?:                    //group, but do not capture (optional):
      \.                   //'.'
      0                    //'0'
    )?                     //end of grouping
  )                        //end of grouping
  $                        //before an optional \n, and the end of the string