IsNumeric Regular Expression

  
using System.Text.RegularExpressions;
 ...

private bool IsNumeric(string s)
{
       Regex r = new Regex(@"^[0-9]+$");
       return r.IsMatch(s);
}

The regular expression defines a pattern and the IsMatch method checks the string to see if it matches the pattern. You can read the regular expression as follows:

^ – start of the string
[0-9] – single digit in the range 0-9
+ – repeat previous item one or more times (single digit)
$ – end of the string

If you are using below Regex for the same purpose

Regex regex = new Regex(@"^\d+$");

please remember that "\d" will match [0-9] and other digit characters like the Eastern Arabic numerals ٠١٢٣٤٥٦٧٨٩. Use "^[0-9]+$" to restrict matches to just the Arabic numerals 0 - 9. It is explained here.