php: converting an array in string

function makestring($array)
{
    if(is_array( $array )) {
        $outval = '';
        foreach($array as $key=>$value)
        {
            if(is_array($value))
            {
                $outval .= makestring($value);
            }
            else
            {
                $outval .= $value;
            }
        }
        return $outval;
    } else {
        die("Supplied argument is not an array");
    }
}
OR 
function makestring( array $array)
{
    // you code goes here
}

Try this. You need to check passing argument is array or not before you use foreach

To prevent an error in foreach, it's better to set type to variable:

foreach((array)$someArray as $data) {

Even if $someArray is not an array, you'll not get any error.

→ Try this:

  function makestring($array)
  {
       $outval = '';
       $keys = array_keys( $array );

       for( $x = 0; $x < count( $array ); $x++ )
       {
            if( is_array( $array[ $keys[ $x ] ] ) )
            {
                 $outval .= makestring( $array[ $keys[ $x ] ] );
            }
            else
            {
                 $outval .= $array[ $keys[ $x ] ];
            }
       }
  return $outval;
  }

Maybe the variables you use $key and $value has old data in them , normally a unset($key,$value) in the end of a foreach will cure that

$array = array(
    '1',
    '2',
    '3',
    array(
        '4',
        '5',
        array(
            '6',
            '7'
        )
    )
);
$output = null;
if(!is_array($array)){
    $array = array($array);
}
// use a reference to the $output in the callback
array_walk_recursive($array, function($array_element) use (&$output){
    if(is_object($array_element) and method_exists($array_element, '__toString')){
        $array_element = strval($array_element);
    }
    if(is_scalar($array_element)){
        $output .= $array_element;
    }else{
        // found a non scalar... handle it! :)
    }
});
echo $output;

Check this out.

array_walk_recursive((array) $array, function($val, $key) {
  global $result;
  $result .= $val;
});

You check via

if(is_array($value))
{
  $outval .= makestring($value);
}

whether to call makestring() recursively. However, in the code that enters makestring() in the first place, you do no such check. That's ok, but then you have to check in makestring(), whether you actually got an array from the caller. That's called defensive programming.

Another option is to do the check on the calling side. That's part of Design By Contract™:

$var = i_usually_give_you_an_array_but_i_might_also_fail();
if (is_array($var)) {
  echo makestring($value);
}

recursive implode() this convert multidimensional array to string

function mYimplode($array, $delimeter) {
 $result='';
 foreach ($array as $key) {
    if (is_array($key)) {
        $result .= mYimplode($key, $delimeter) . $delimeter;
    } else {
        $result .= $key . $delimeter;
    }
 }

 $result = substr($result, 0, 0-strlen($delimeter));

 return $result;
}