validation: '@' cannot be more than one character

Question

I can't get the logic of this problem from my mind. Will you help me, pls?

I make a manual email validation for practice. So, in email validation there's a validation that states: "@ is cannot be more than one."

I'm stuck from here:

            int atValidation = 0;
        for (int i = 0; i < txtEmail.Text.Length; i++)
        {
            if (Char.IsSymbol('@'))
            {
                atValidation++;
            }
        }

Can you clarify your question? I'm a little confused. Also, how is the above code *supposed* to work? is it trying to figure out if there's more than one "@" symbol in the string? — EJoshuaS - Stand with Ukraine, Aug 16 '16 at 18:30
Also, are you implementing other validation rules as well (or just this one)? How are you defining a "valid" email address? Can you give examples of email addresses you want to accept and ones you want to reject? — EJoshuaS - Stand with Ukraine, Aug 16 '16 at 18:40
Possible duplicate of [Using a regular expression to validate an email address](http://stackoverflow.com/questions/201323/using-a-regular-expression-to-validate-an-email-address) — Stanfrancisco, Aug 16 '16 at 18:43
Your only question is "Will you help me, pls". What exactly do you want? — Sergey.quixoticaxis.Ivanov, Aug 16 '16 at 19:20

score 1 · Answer 1 · answered Aug 16 '16 at 18:41

There are many more rules for email validation, but if all you want to do is check for a single @ sign, you could get all of the @ characters and check the count

if (txtEmail.Text.ToCharArray().Where(x => x == '@').Count() != 1)
{
     //email is invalid
}

score 1 · Answer 2 · edited May 23 '17 at 11:52

1

There are other better ways to validate email for example MailAddress class and regex.

You can find examples here:

MailAddress: Regex Email validation

regex: Best Regular Expression for Email Validation in C#

edited May 23 '17 at 11:52

Community

1
1

answered Aug 16 '16 at 18:41

Vivek Sharma

1,912
1
13
15

And most of them don't validate every email possible. The best email validation is sending something to it. – Sergey.quixoticaxis.Ivanov Aug 16 '16 at 19:21

EJoshuaS - Stand with Ukraine · Answer 3 · 2016-08-16T18:55:11.200

There are a few ways you can do this. The first example I show below is a "straight" LINQ query and the second is an extension method that uses a loop. (Extension methods, in case you're not familiar, are a way of "adding" a method to class without modifying the original code; it's a Decorator Pattern).

LINQ Query approach:

int count = email.Count(c => c == '@');

This will give you the number of times that the '@' symbol appears. If count > 1 you know that there are duplicates. (Actually, you'd expect "count" to be exactly 1; if it's 0 there's no '@' symbol at all).

The downsides of the above solution are that it isn't very flexible (if you wanted to implement more rules you'd effectively be doing more loops, which isn't all that efficient) and that it'll always go through the entire string; it's not "smart enough" to know that it can stop counting once count == 2.

Here's another one:

public static class LinqExtensions
{
    public static bool ContainsMultiple<T>(this IEnumerable<T> enumerable, T item)
    {
        bool seen = false;

        foreach (T t in enumerable)
        {
            if (t.Equals(item))
            {
                if (seen) return true;
                else seen = true;
            }
        }

        return false;
    }
}

You use it like this:

bool multiple = email.ContainsMultiple('@');

This solution also suffers from some degree of inflexibility (the only way to check multiple rules is to implement multiple loops/queries). However, it's "smart" enough to know that you can stop searching the string once you find a duplicate. It's also reusable.

You could also do:

validation: '@' cannot be more than one character

3 Answers3