Remove several dots/commas in string from every decimal number

Question

How can I check for a comma in a number?

Lets assume I have a string which represents a polynomial term that looks like this

string x = "x+1+5,54";

Now the user wants to put in and add a comma which will then be "x1+5,54," which is not a number anymore. How can I check this with an if?

Something like if the last number already contains a comma don't append another one.

Answer 1

Use regular expression.

        if (Regex.IsMatch(a, @"^((\d+,?\d*)|(\w?))([-+/]((\d+,?\d*)|(\w?)))*$"))
        {
            //correct
        }
        else
        {
            //incorrect
        }

You'll get false, when user inputs extra comma, so you can handle it.