PHP接收不到函数返回值。。

[sophialeo1314]

for ($i = 0; $i < 30; $i++) {
$arr[$i] = $i;
}

var_dump(BinarySearch($arr, 100, 0, count($arr) - 1));


function BinarySearch ($arr, $searchVal, $leftIndex, $rightIndex) {

if ($rightIndex < $leftIndex) {
return 'ERROR';
}

$midIndex = round(($leftIndex + $rightIndex) / 2);
$midVal = $arr[$midIndex];
if ($searchVal < $midVal) {
BinarySearch($arr, $searchVal, $leftIndex, $midIndex - 1);
} else if ($searchVal > $midVal) {
BinarySearch($arr, $searchVal, $midIndex + 1, $rightIndex);
} else {
return $midIndex;
}

}

代码如上，var_dump出来的结果是空，但是如果把BinarySearch里面的两个return语句改成echo浏览器又能正常输出了，到底是哪出了问题？

[xuzuning]

function BinarySearch ($arr, $searchVal, $leftIndex, $rightIndex) {
  if ($rightIndex < $leftIndex) {
    return 'ERROR';
  }
  $midIndex = round(($leftIndex + $rightIndex) / 2);
  $midVal = $arr[$midIndex];
  if ($searchVal < $midVal) {
    return BinarySearch($arr, $searchVal, $leftIndex, $midIndex - 1); //这里需要返回
  } else if ($searchVal > $midVal) {
    return BinarySearch($arr, $searchVal, $midIndex + 1, $rightIndex); //这里也需要返回
  } else {
    return $midIndex;
  }
}