c# regex and [] expression , why does [+*/-] fail to parse?

Question

i tried to use Regex in c# , but the following code throws an exception:

string pattern = "(\d+)([+*/-])(\d+)";

Regex reg = new Regex  (pattern);

After a little dig , i found that in c# if you try to match '-' with [] expression , it must be put as the first character in that bracket , which confused me.

Could someone jump out and explain that to me ?

Appreciate any of your responses.

Answer 1

The - character takes on a special meaning within a character class [...] to denote a range, so that shorthand expressions like the following work:

"[a-z]" // matches all lowercase alphabetic characters without having to specify them all.

The - is only interpreted literally if it is the first character simply because it can't denote a range because no other value precedes it.

Honestly, it should make no difference whether it is the first or the last character.