// Returns the next higher or lower number
function NextRelatedNumber($number, $range){  
  $r = $number % $range;
  $f = $number - $r;
  $b = round($r / $range, 0);
  return ($b == 1) ? $f + $range : $f;  
}
// Returns the next higher number
function NextHigherNumber($number, $range){  
  $r = $number % $range;
  $f = $number - $r;
  $b = ceil($r / $range);
  return ($b == 1) ? $f + $range : $f;  
}
// Returns the next lower number
function NextLowerNumber($number, $range){  
  $r = $number % $range;
  $f = $number - $r;
  $b = floor($r / $range);
  return ($b == 1) ? $f + $range : $f;  
}
// Returns the next related number from an array
function NextNumberArray($Number, $NumberRangeArray){
  $w = 0;
  $c = -1;
  $abstand = 0;
  $l = count($NumberRangeArray);    
  for($pos=0; $pos < $l; $pos++){
    $n = $NumberRangeArray[$pos];
    $abstand = ($n < $Number) ? $Number - $n : $n - $Number;
    if ($c == -1){
      $c = $abstand;
      continue;
    }
    else if ($abstand < $c){
      $c = $abstand;
      $w = $pos;
    }
  }
  return $NumberRangeArray[$w];
}
 
// Examples
// --------
// 0 10 20 30 40 50 ...
print 'NextRelatedNumber: ';
print NextRelatedNumber(44, 10) . "\n";
// returns --> 40
// 0 20 40 60 80 100 ...
print 'NextHigherNumber: ';
print NextHigherNumber(41, 20) . "\n";
// returns --> 60
// 0 5 10 15 20 25 30 35 ...
print 'NextLowerNumber: ';
print NextLowerNumber(57, 5) . "\n";
// returns --> 55
// Example with Array
print 'NextNumberArray: ';
print NextNumberArray(45, array(3, 8, 19, 34, 56, 89)) . "\n";
// returns --> 34
// (45 is between 34 and 56 but 34 is the next)