Notes on using regexes in C#

regexes_notes.cs

https://regex101.com/r/3v4pjk/1

new Regex(@"^([A-Za-z]{2}(\d)(|\-))([A-Za-z]{3})-(\d)(\d)(\d)$)")
new Regex(@"^([A-Za-z]{2}(\d)(|\-))([A-Za-z]{3})-(\d)(\d)(\d)$)")


new Regex(@"
^ # start of line
[A-Za-z]{2} # two letters
\d # one digit
\- # hyphen
[A-Za-z]{3} # three letters
\- # hyphen
\d{3} # three digits
$ # end of line
)")

the pipe symbol before the first hyphen matches nothing or a hyphen - this means it will also match `aa6aaa-123`

a hyphen doesn't need escaping (escape = put a \ in front, so for e.g. the `\d` it doesn't match a d but instead looks for a single number)

new Regex(@"^[A-Za-z]{2}\d-[A-Za-z]{3}-\d{3}$")
Demo via https://regex101.com/r/3v4pjk/1

http://www.mikesdotnetting.com/Article/46/c-regular-expressions-cheat-sheet

you don't need the pipe symbol | or brackets in there, but for clarity you can wrap the number/letter combinations in brackets, e.g. 

new Regex(@"^([A-Za-z]{2}\d)-([A-Za-z]{3})-(\d{3})$")

capturing groups - matches[0].groups etc
each section in () is a capturing group
you can refer to these as \0 \1 etc


http://stackoverflow.com/questions/3665757/how-to-convert-char-to-int


int one = numbers[0];


					int a = (int)Char.GetNumericValue(numbers[0]);
                    Console.WriteLine(a);
                    int b = (int)Char.GetNumericValue(numbers[1]);
                    int cee = (int)Char.GetNumericValue(numbers[2]);
                    int d = numbers[3];
                    int e = a + b + cee;
                    Console.WriteLine(e);
                

all the numbers separately in groups:
^[A-Za-z]{2}(\d)-[A-Za-z]{3}-(\d)(\d)(\d)$