Question

Could anyone please help with C# regular expression for requirement below, please?

1. should start with 1 and should be 6 digit long.
2. should start with 7 and should be 6 digit long.
3. should be 8 digit long.

Update:
Apologies not clarifying the requirement. They are individual cases ie. all I need is a regular expression to these specific cases (i.e. 3 in total).

Answer 1

Here it is:

^((1|7)\d{5}|\d{8})$

or following NullUserException ఠ_ఠ advice:

^([17]\d{5}|\d{8})$