How is it wrong to write two-point lookups?

What's wrong with writing two-point lookups?

 
  
function BinarySearch ($arr, $a) {
    
    $low = 0;
    $high = count ($arr)-1;
    $mid = Ceil (($low + $high)/2);

while ($low <= $high) {

    if ($a = = $arr [$mid]) {
    echo "The location of the number to find is". " $mid ";
    }

    if ($a > $arr [$mid]) {

        $high = count ($arr)-1;
    $low = $mid +1;
    $mid = Ceil (($low + $high)/2);
    }

    if ($a < $arr [$mid]) {
    
    $low = 0;
    $high = $mid-1;
    $mid = Ceil (($low + $high)/2);
    }
  }
}
$arr 1 = array (5,7,9,10,12,16,19);
BinarySearch ($arr 1,12);

?>

------Solution--------------------
This post was last edited by xuzuning on 2013-03-30 17:42:33

function BinarySearch ($arr, $a) {

$low = 0;
$high = count ($arr)-1;
$mid = Ceil (($low + $high)/2);
$n = 0;Measures to prevent the death cycle
while ($low <= $high && $n + + ){
if ($a = = $arr [$mid]) {
echo "The location of the number to find is". " $mid ";
Break
}

if ($a > $arr [$mid]) {

$high = count ($arr)-1;
$low = $mid -1; //Note here
$mid = Ceil (($low + $high)/2);
}

if ($a < $arr [$mid]) {

$low = 0;
$high = $mid +1; //Note here
$mid = Ceil (($low + $high)/2);
}
}
}
------Solution--------------------
By PHP actually can write

function BinarySearch ($arr, $a) {
  $low = 0;
  $high = count ($arr)-1;
  $mid = Ceil (($low + $high)/2);
  $num = count ($arr);
  while ($low <= $high && $num-) {
    if ($a = = $arr [$mid]) {
      echo "The location of the number to find is". " $mid ";
      Break
    }
    List ($low, $high) = $a > $arr [$mid]? Array ($mid, $high): Array ($low, $mid);
    $mid = Ceil (($low + $high)/2);
  }
}

------Solution--------------------

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