function implode ($glue = "", array $pieces) {}

$test = array("hello","world","php");
echo implode("-",$test);

$test = array("h"=>"hello","w"=>"world","p"=>"php");
echo implode("-",$test);

function explode ($delimiter, $string, $limit = null) {}

$str="hello-world-php";
$result = explode("-", $str);
var_dump($result);
$result = explode("-", $str,2);
var_dump($result);

array(3) {
  [0]=>
  string(5) "hello"
  [1]=>
  string(5) "world"
  [2]=>
  string(3) "php"
}
array(2) {
  [0]=>
  string(5) "hello"
  [1]=>
  string(9) "world-php"
}

**
 * Convert a string to an array
 * @link http://php.net/manual/en/function.str-split.php
 * @param string $string <p>
 * The input string.
 * </p>
 * @param int $split_length [optional] <p>
 * Maximum length of the chunk.
 * </p>
 * @return array If the optional split_length parameter is
 * specified, the returned array will be broken down into chunks with each
 * being split_length in length, otherwise each chunk
 * will be one character in length.
 * </p>
 * <p>
 * false is returned if split_length is less than 1.
 * If the split_length length exceeds the length of
 * string, the entire string is returned as the first
 * (and only) array element.
 * @since 5.0
 */
function str_split ($string, $split_length = 1) {}

$str = "hello";
var_dump(str_split($str,2));
1
2


array(3) {
  [0]=>
  string(2) "he"
  [1]=>
  string(2) "ll"
  [2]=>
  string(1) "o"
}