What are the different methods to convert a timestamp into a date/time and vice versa in PHP?

When working with timestamps and dates in PHP, it is common to need to convert between the two formats. To convert a timestamp into a date/time, you can use the `date()` function with the appropriate format specifier. To convert a date/time into a timestamp, you can use the `strtotime()` function.

// Convert timestamp to date/time
$timestamp = time(); // current timestamp
$date = date('Y-m-d H:i:s', $timestamp);
echo $date;

// Convert date/time to timestamp
$date = '2022-01-01 12:00:00';
$timestamp = strtotime($date);
echo $timestamp;