Question

I’m using C#.
How would I verify whether an input string is an integer and is only made up of digits 0-9?

An additional requirement is that it should be always made up of exacly 9 digits total; no more, no less.

e.g.,

OK: 118356737, 111111111, 123423141,

ERROR: 11a334356,
1.2.4.535,
1112234.222 etc

thanks

Answer 1

You can use either regex:

string input = "123456789";
bool isValid = Regex.IsMatch(input, @"^\d{9}$");

or LINQ:

string input = "123456789";
bool isValid = input.Length == 9 && input.All(char.IsDigit);