Detailed explanation of PHP 5.2.x array operation examples

ArrayOperations in php 5.2.x

I just watched the php introductory tutorial and summarized some php array operations caused by different php versions. question.

The following content was tested in the php5.2.5 environment.
1,

<?php
$arr = array("a" => 1,"b" => 2,"c" => 3);

If you define an array like this, a compilation error will be reported:

Copy code code example:

<?php
$arr = array("a" = 1,"b" = 2,"c" = 3);

Therefore, when defining an array, you can only use =>

Copy code example:

<?php
$arr = array("a" => 1,"b" => 2,"c" => 3);
echo $arr[0];
echo $arr[1];

What is typed is Blank.

Correct printing method:

Copy code Code example:

echo $arr["a"];

3. Add elements Or when modifying elements, you can only use =, not =>

Copy code Code example:

<?php
$arr = array("a" => 1,"b" => 2,"c" => 3);
$arr["c"] => 6;

The above operation method, A compilation error will occur in php 5.2.5

To add elements or modify elements, write like this:

Copy code code example:

<?php
$arr = array("a" => 1,"b" => 2,"c" => 3);
$arr["d"] = 4;
$arr["c"] = 6;

To delete elements, use unset:

Copy code Code example:

unset ($arr["c"]);

4. Think about the following code, what will be output?

Copy code Code example:

<?php
$arr = array("a" => 1,2,"b" => 3,4);
$arr[] = 5;
foreach($arr as $key => $value)
{
    echo "key:$key value:$value<br>";
}

Output result:

key:a value:1
key:0 value:2
key:b value:3
key:1 value:4
key:2 value:5

Description: Only if When the user does not define a key, PHP will automatically use a number starting from 0 as the key.

5. Arrays in php have pointers, and you can perform forward and backward operations on the array

Copy code code example:

<?php
$arr = array("a" => 1,3,"b" => 2);

//Create After completing the array, the default pointer points to the first element
echo current($arr)."
";
//Advance one position
echo next($arr )."
";
//The default principle of sorting is from small to large
sort($arr);
//After sorting, the array pointer stops at the first element
echo current($arr)."
";
echo next($arr)."
";
//Go back one position
echo prev($arr). "
";

Output result:

13121

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