Question

I need a regular expression for my password format. It must ensure that password only contains letters a-z, digits 0-9 and special characters: .@#$%&.
I am using .NET C# programming language.
This is my code:

Regex userAndPassPattern = new Regex("^[a-z0-9.@#$%&]$");
if (!userAndPassPattern.IsMatch(username) || !userAndPassPattern.IsMatch(password))
    return false;

The problem is that I always get back false.

Answer 1

!A || !B is logically equivalent to !(A && B)

So you could write better

!(userAndPassPattern.IsMatch(username) && userAndPassPattern.IsMatch(password))

Then you have a special character $ in you character class, maybe you need to mask it \$
I’m not quite sure about this, because in a character class it is not a special character. Maybe it depends on the RegEx engine in use. If you mask the $ it should do no harm ([a-z0-9.@#\$%&])

Then you have just a single character to match. You need a quantifier

[a-z0-9.@#$%&] means one single character out of the given, will match aor b or 0 but not ab
[a-z0-9.@#$%&]+ many characters out of the given, from 1 to endless appearances, will match a, b, and ab and ba etc.

edit

This is what you want

Regex userAndPassPattern = new Regex("^[a-z0-9\.@#\$%&]+$");
if (!(userAndPassPattern.IsMatch(username) && userAndPassPattern.IsMatch(password))) {
    return false;
}