You're already storing it like that (more or less).
$str ="This is a test string";
echo "Array
(
";
for($i = 0; $i < strlen($str); $i++)
{
echo "[$i] => " . $str[$i] . "\n";
}
echo ")";
output:
Array
(
[0] => T
[1] => h
[2] => i
[3] => s
[4] =>
[5] => i
[6] => s
[7] =>
[8] => a
[9] =>
[10] => t
[11] => e
[12] => s
[13] => t
[14] =>
[15] => s
[16] => t
[17] => r
[18] => i
[19] => n
[20] => g
)
EDIT: My code above was just an example to show you that strings can be accessed as if they were character arrays without any need to convert the string itself.
If you really have a specific need for an array of characters rather than a string, however, you could always use the [man]str_split/man function.
