Administrative way of adding and substracting months in PHP

dateCalc.php

<?php
  // FUNCTION 1 (without leap check?)
  //////////////////////////////////////
  $date=new DateTime();
  $date->setDate(2008,2,29);

  function addMonths($date,$months){

    $init=clone $date;
    $modifier=$months.' months';
    $back_modifier =-$months.' months';

    $date->modify($modifier);
    $back_to_init= clone $date;
    $back_to_init->modify($back_modifier);

    while($init->format('m')!=$back_to_init->format('m')){
      $date->modify('-1 day')    ;
      $back_to_init= clone $date;
      $back_to_init->modify($back_modifier);    
    }

    /*
    if($months<0&&$date->format('m')>$init->format('m'))
    while($date->format('m')-12-$init->format('m')!=$months%12)
    $date->modify('-1 day');
    else
    if($months>0&&$date->format('m')<$init->format('m'))
    while($date->format('m')+12-$init->format('m')!=$months%12)
    $date->modify('-1 day');
    else
    while($date->format('m')-$init->format('m')!=$months%12)
    $date->modify('-1 day');
    */
        
  }
  function addYears($date,$years){

    $init=clone $date;
    $modifier=$years.' years';
    $date->modify($modifier);

    while($date->format('m')!=$init->format('m'))
      $date->modify('-1 day');
    } 
  }
    addMonths($date,-1);
    addYears($date,3);
    echo $date->format('F j,Y');


  // FUNCTION 2 (with leap check?)
  //////////////////////////////////////
  $d = new DateTime('2007-12-31');

  function addMonths($date, $months)
  {
    $years = floor(abs($months / 12));
    $leap = 29 <= $date->format('d');
    $m = 12 * (0 <= $months?1:-1);
    for ($a = 1;$a < $years;++$a) {
        $date = addMonths($date, $m);
    }
    $months -= ($a - 1) * $m;

    $init = clone $date;
    if (0 != $months) {
        $modifier = $months . ' months';

        $date->modify($modifier);
        if ($date->format('m') % 12 != (12 + $months + $init->format('m')) % 12) {
            $day = $date->format('d');
            $init->modify("-{$day} days");
        }
        $init->modify($modifier);
    }

    $y = $init->format('Y');
    if ($leap && ($y % 4) == 0 && ($y % 100) != 0 && 28 == $init->format('d')) {
        $init->modify('+1 day');
    }
    return $init;
  }

  function addYears($date, $years)
  {
    return addMonths($date, 12 * $years);
  }

  echo $d->format('F j,Y') . ' N<br />';
  $d = addMonths($d, +1);
  echo $d->format('F j,Y') . ' +1M<br />';
  $d = addMonths($d, +1);
  echo $d->format('F j,Y') . ' +1M<br />';
  $d = addYears($d, +60);
  echo $d->format('F j,Y') . ' +60Y<br />';
  $d = addYears($d, -59);
  echo $d->format('F j,Y') . ' -59Y<br />';