php 基础知识

    $str1 = null;
    $str2 = false;
    echo $str1==$str2 ? ‘相等‘ : ‘不相等‘;
    $str3 = ‘‘;
    $str4 = 0;
    echo $str3==$str4 ? ‘相等‘ : ‘不相等‘;
    $str5 = 0;
    $str6 = ‘0‘;
    echo $str5===$str6 ? ‘相等‘ : ‘不相等‘;　

$a1 = null;
    $a2 = false;
    $a3 = 0;
    $a4 = ‘‘;
    $a5 = ‘0‘;
    $a6 = ‘null‘;
    $a7 = array();
    $a8 = array(array());
    echo empty($a1) ? ‘true‘ : ‘false‘;
    echo empty($a2) ? ‘true‘ : ‘false‘;
    echo empty($a3) ? ‘true‘ : ‘false‘;
    echo empty($a4) ? ‘true‘ : ‘false‘;
    echo empty($a5) ? ‘true‘ : ‘false‘;
    echo empty($a6) ? ‘true‘ : ‘false‘;
    echo empty($a7) ? ‘true‘ : ‘false‘;
    echo empty($a8) ? ‘true‘ : ‘false‘;

 $test = ‘aaaaaa‘;
    $abc = & $test;
    unset($test);
    echo $abc;

 $count = 5;
    function get_count(){
        static $count = 0;
        return $count++;
    }
    echo $count;
    ++$count;
    echo get_count();
    echo get_count();

$arr=[1,6,3,8,9,12,6];
$len=count($arr);

for($i=0;$i<$len;$i++)
{
  for($j=$i+1;$j<$len;$j++)
  {

    if($arr[$i]>$arr[$j])
    {
       $tmp=$arr[$i];
       $arr[$i]=$arr[$j];
       $arr[$j]=$tmp;

    }

  }
}

var_dump($arr);

function  binarySearch(Array $arr,$key)
   {
        $len=count($arr);
        if($len==0)
            return false;
        $begin=0;
        $end=$len-1;

        //如果查找的值为集合首元素则$begin,$end将=
        while ( $begin <= $end) {

          $mid=floor(($begin+$end)/2);
          if($arr[$mid]==$key){
               return  $arr[$mid];
          }
          if($arr[$mid]<$key){
            $begin=$mid +1;
          }
          if($arr[$mid]>$key){
             $end=$mid-1;
          }
       }
        return false;
  }
 $arr=[3,4,6,7,8,10,11,55,67];
 $result=binarySearch($arr,4);
 var_dump($result);