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Master four ways to loop through arrays

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Release: 2023-03-10 16:18:02
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[(Key) Four ways of circulating through arrays] <br> 1. <br>## conut($arr); used to count the number of array elements. <br> The for loop can only be used to traverse, pure index arrays! ! ! ! <br> If there is an associative array, the total number of the two arrays will be counted during count statistics, and a for loop will be used to traverse the mixed array, causing the array to go out of bounds! ! <br> eg:<br> $arr = array(1,2,3,5,6,7);<br> $num = Count ($ Arr); // Count is best placed outside the outside, which can allow the function to execute only ## Echo. br/>";<br> for($i=0;$i<$num;$i++){
echo "{$i}==> ;{$arr[$i]}
";<br> }<br> <br> <br> 2. forEach loops through the array foreach can traverse any type of array! ! ! <br> eg: <br>

 $arr = array(1,2,3,"one"=>4,5,6,7);   foreach($arr as $value){
  echo "{$item}<br>";
 } foreach($arr as $key => $value){
  echo "{$key}==>{$item}<br>";
 }
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<br>##An example is as follows Array:

$h51701 ==>=>,=>,=>=>,=>,=>=>,=>,=>=>=>,=>,=>=>,=>,=>=>,=>,=>=>=>,=>,=>=>,=>,=>=>,=>,=> ($h51701  $key => ($value  $key1 =>.($key1+). ($value1  $key2 =>
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<br>   使用list()、each()、while()遍历数组<br>   (重点)list():用于将数组的每一个值,赋值给list函数的每一个参数。(list函数的参数,必须小于等于数组的元素个数);<br>   eg:list($a,$b,$c)=[1,2,3];-->$a=1; $b=2; $c=3;<br>   注意:① list()在解析数组时,只解析索引数组;<br>        ② list可以通过空参数,选择性的解析数组的值;<br>          list($a,,$b)=[1,2,3];-->$a=1;  $b=3;<br>   (重点)each():用于返回数组当前指针所在位的键值对!并将指针后移一位;<br>       返回值:如果指针有下一位,返回一个数组。包含一个索引数组(0-键,1-值)和一个关联数组("key"-键,"value"-值);如果指针没有下一位,返回false;         <br>   eg: <br>    ① each($arr) 返回数组或false;<br>    ② 把数组或false赋值给$a;<br>    ③ while判断$a如果是数组,继续执行下一次;<br>             如果$a是false,终止循环<br>  while($a = each($arr)){<br>  echo "{$a[0]}-->{$a[1]}<br>";  <br>  echo "{$a['key']}-->{$a['value']}<br>";  <br>  } <br>   3.使用list()/each()/while()配合遍历数组

 while(list($key,$value) = each($arr)){
   echo "{$key}-->{$value}<br>";  
      }
     reset($arr);
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     !!!!数组使用each()遍历完一遍后,指针使用处于最后一位的下一位;即再用each(),始终返回false;<br>     如果还需使用,需用reset($arr);函数,重置数组指针;<br>  eg:

 $arr = array(1,2,3,"one"=>4,5,6,7);   foreach($arr as $value){
  echo "{$item}<br>";
 } foreach($arr as $key => $value){
  echo "{$key}==>{$item}<br>";
 }
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 (=
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 while(list($key,$value) = each($arr)){
  echo "{$key}-->{$value}<br>";  
  }
  reset($arr);  while(list($key,$value) = each($arr)){
  echo "{$key}-->{$value}<br>";  
  }
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<br>  4、 使用数组指针遍历数组<br>   ① next:将数组指针,后移一位。并返回后一位的值;没有返回false<br>   ② prev:将数组指针,前移一位。并返回前一位的值;没有返回false<br>   ③ end:  将数组指针,移至最后一位,返回最后一位的值;空数组返回false<br>   ④ reset:将数组指针,恢复到第一位。并返回第一位的值;空数组返回false<br>   ⑤ key: 返回当前指针所在位的键;<br>   ⑥ current:返回当前指针所在位的值;

$arr = [,,,,=>((!
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do{
   echo key($arr);
   echo "--";
   echo current($arr);
  echo "<br>";
  }while(next($arr));
  reset($arr);
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<br>
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  牛刀小试:<br>   1.遍历数组:$subject1 = array("Linux","PHP","MySQL","HTML","CSS","JQuery")<br>  方式一:for循环遍历

for($i=0;$i<count($subject1);$i++){
     echo $subject1[$i]."<br/>";
   }
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  方式二:使用list()/each()/while()配合遍历数组

 .
(list($key,$value)=
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方式三:forEach循环遍历

foreach ($subject1 as $key => $value) {
   echo "{$key}-->{$value}<br/>";
  }
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 方式四:指针

 do{<br>   echo   key($subject1)."=>".current($subject1)."
";<br>  }while(next($subject1));<br>  echo "
";
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2.使用reset(),end(),prev(),next(),key(),current();与do…while组合倒着输出数组中的值:<br>  $subject2 = array(“Linux”,”PHP”,”MySQL”,”HTML”,”CSS”,”JQuery”)

 $subject2 = array("Linux","PHP","MySQL","HTML","CSS","JQuery");
    end($subject2);   do{
   echo key($subject2)."=>".current($subject2)."<br>";
  }while(prev($subject2));
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     <br> 

感觉不错就试试吧!!!

  <br> 

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