How to implement unsubscribe feature for website?

hie zoran i check it has correct answer for this post and my previous post
thanks
karthik

Karthik if your query is resolved, mark Zoran's answer as 'Answered'.

Ya sure Zoran iam working now if their any doubts i will contact u

Please don't forget to check "This is correct answer" for the post which helped you solve the problem.

Thanks,
Zoran

thanq  zoran thanq very much

rnd.Next(26) would generate random integer in range 0 to 25 inclusive. Now adding 'A' to that (actually adding ASCII code for 'A') would make 'A' from value 0, 'B' from 1, ... , 'Z' from 25. In that way I'm appending one letter at a time to the string builder and all letters are randomly generated.

Zoran

hie
thanq awesome explanation
Now that this is done, remaining length - sb.Length characters are completely randomly generated:
while (sb.Length < length)
    sb.Append((char)(rnd.Next(26) + 'A'));
can u explain this line

First I'm creating a string which contains current UTC timestamp up to 1/10,000 seconds:
string ts = DateTime.UtcNow.ToString("yyyyMMddHHmmssffff");

This would produce output:
201107261016464723
, which is year 2011, month 07, day 26, hour 10, minute 16, second 46 and part of the second 4723

Now this string, which consists of digits, is converted to letters so that 0 becomes A, 1 becomes B, ..., 9 becomes I:
for (int i = 0; i < ts.Length; i++)
    sb.Append((char)(ts[i] - '0' + 'A'));

Now that this is done, remaining length - sb.Length characters are completely randomly generated:
while (sb.Length < length)
    sb.Append((char)(rnd.Next(26) + 'A'));

In this way you get string of required length which consists of current UTC timestamp and random part, e.g.:
CABBAHCGBABIEAAHBHPSYWUJYKHIYY

This should always be unique (unless you have more than 16 new customers per second, as clock changes 15-16 times per second).

Zoran

hie
thanq thanq very much i will try it if their any doubts i will contact you zoran
 yesterday i tried your storedprocedure its working now

hie
can u explain this code plz dont mind
private string GenerateToken(int length)
{

    Random rnd = new Random();
    StringBuilder sb = new StringBuilder();

    string ts = DateTime.UtcNow.ToString("yyyyMMddHHmmssffff");

    for (int i = 0; i < ts.Length; i++)
        sb.Append((char)(ts[i] - '0' + 'A'));

    while (sb.Length < length)
        sb.Append((char)(rnd.Next(26) + 'A'));

    return sb.ToString();

}

I don't have ready to use code, but it should not be too complicated to implement.

Function which generates token can look like this:
private string GenerateToken(int length)
{

    Random rnd = new Random();
    StringBuilder sb = new StringBuilder();

    string ts = DateTime.UtcNow.ToString("yyyyMMddHHmmssffff");

    for (int i = 0; i < ts.Length; i++)
        sb.Append((char)(ts[i] - '0' + 'A'));

    while (sb.Length < length)
        sb.Append((char)(rnd.Next(26) + 'A'));

    return sb.ToString();

}

private string GenerateToken()
{
    return GenerateToken(40);
}

You can use GenerateToken() function and that will generate 40 characters long tokens. First part of the token is created from current timestamp which guarantees uniqueness.

Now suppose that you have a customers table like this:
CREATE TABLE Customer(
    CustomerID INT PRIMARY KEY IDENTITY(1, 1),
    UserName VARCHAR(100),
    MailingListToken CHAR(40)
);

In this case, you can create Subscribe and Unsubscribe stored procedures:
CREATE PROCEDURE Subscribe
    @CustomerID INT,
    @Token CHAR(40)
AS
BEGIN
    UPDATE Customer SET MailingListToken=@Token WHERE CustomerID=@CustomerID
END
GO

CREATE PROCEDURE Unsubscribe
    @Token CHAR(40)
AS
BEGIN
    UPDATE Customer SET MailingListToken=NULL WHERE MailingListToken=@Token
END
GO

You can extract the list of subscribed customers like this:
SELECT CustomerID, UserName FROM Customer WHERE MailingListToken IS NOT NULL;

Zoran

hie Zoran,
What you said i understand
But How to write code for this Token should be a relatively long string which is randomly generated and unique
If you know can u write code for me
If you have any example application or just sample overview  regarding this task will you post for me