How do I count unique visitors to my site?

There are several ways to count unique visitors to a website using PHP, but one common method is to use cookies.

1. Set a cookie on the user's browser when they first visit your site.
2. Check for the existence of this cookie on subsequent page loads.
3. If the cookie does not exist, increment a counter and set the cookie.
4. If the cookie does exist, do not increment the counter.

You can also use IP address to identify unique visitors, but this method has limitations as many users share IP addresses.

Another way to do this is by using sessions instead of cookies. You can set a session variable when a new user visits your site and check for the existence of this session variable on subsequent page loads. If the session variable does not exist, increment a counter and set the session variable. If the session variable does exist, do not increment the counter.

You can also use a database to store the unique visitor count. You can store the user's IP address and a timestamp in a table and check for the existence of a matching IP address with a timestamp that is within a certain time frame (i.e. the last 24 hours). If a match is not found, increment the visitor count in the database and insert the IP address and timestamp.