how to get the one month from the actual day php code example

Example 1: get day of month php

// get day of month php
// Method 1; some server not work, I had check php 7.3.24 not worked, php 7.3.8 worked
cal_days_in_month(CAL_GREGORIAN, $month, $year)
echo (cal_days_in_month(CAL_GREGORIAN, 2, 2020)); // => 29

// Method 2;
function days_in_month($month, $year) {
    // calculate number of days in a month
    return $month == 2 ? ($year % 4 ? 28 : ($year % 100 ? 29 : ($year % 400 ? 28 : 29))) : (($month - 1) % 7 % 2 ? 30 : 31);
}

// Method 3;
echo (date('t', strtotime('2020-02-1')));	// 29

Example 2: in date function + 1 month and - 1 day in php

<?php
$months = n; // Here n = …..-2,-1,0,1,2, …..(months to add or subtract)
$years = n;  // Here n = …..-2,-1,0,1,2, …..(years to add or subtract)
echo date('Y-m-28', mktime(0, 0, 0, date('m')+$months, 1, date('Y') + $years));
?>