Date _ php tips for the day before or after php

Php determines the code of the day before or before today. The code is as follows:

Date_default_timezone_set ('prc'); // Default time zone
Echo "today:", date ("Y-m-d", time ()),"
";
Echo "today:", date ("Y-m-d", strtotime ("18 Jun 2008 ")),"
";
Echo "yesterday:", date ("Y-m-d", strtotime ("-1 day ")),"
";
Echo "tomorrow:", date ("Y-m-d", strtotime ("+ 1 day ")),"
";
Echo "one week later:", date ("Y-m-d", strtotime ("+ 1 week ")),"
";
Echo "one week, two days, four hours, two seconds later:", date ("Y-m-d G: H: s ", strtotime ("+ 1 week 2 days 4 hours 2 seconds ")),"
";
Echo "next Thursday:", date ("Y-m-d", strtotime ("next Thursday ")),"
";
Echo "last Monday:". date ("Y-m-d", strtotime ("last Monday "))."
";
Echo "a month ago:". date ("Y-m-d", strtotime ("last month "))."
";
Echo "one month later:". date ("Y-m-d", strtotime ("+ 1 month "))."
";
Echo "Ten years later:". date ("Y-m-d", strtotime ("+ 10 year "))."
";
?>

Php determines the number of days before a date.

The code is as follows:

Echo (strtotime ('1970-5-20 ')-strtotime (date ("Y-m-d")/2020; then
?>