Regex for matching expression that consists of single digit numbers and operators – codereview.stackexchange.com #JHedzWorlD

I would like to create a regex that will validate that a string is an equation made up of a single digits and either the * or + operator and is no longer than 100 characters. So these would be valid:

1+2*3*8+0 9 9*9 

And these would not be valid:

1++1 12+1 2*25 1+ 47 + +1 11 

I came up with the regex below to accomplish this:

^(d1[+*]1)0,99d$ 

Which appears to work, but I’m curious if there is a cleaner way to accomplish this. Any suggestions or is this about as clean as it gets?

It is saved here if you would like to play with it.

• While your regex appears to work, it will fail for the condition that your expression should not exceed 100 characters mark. With the boundary of 0,99 on a 2 character pattern d1[*+]1, you are already expecting a possible expression of length 198 characters.


• Using 1 quantifier is just redundant.


• No need for escaping inside a character set. The only things needing a leading backslash () inside a characters list are ] and ^, where the caret is the only character inside, or the first.


• Your expressions will not reach a 100 character mark, unless you allow the + to act as an unary operator.

Therefore, the following pattern will be the simplest approach (imo)

^(?:d[*+])0,49d$ 

which is the tiniest bit modified from your original expression.

You can check the pattern in action here on the following expressions:

1+2*3*8+0 9 9*9 1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+5*8 1++1 12+1 2*25 1+ 47 + +1 11 1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+5*8+9 

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Regex for matching expression that consists of single digit numbers and operators – codereview.stackexchange.com #JHedzWorlD