[Solved] How performing these two function?

Use preg_match to capture them in your functions.

Regex for capturing the letters:

/([A-Z]+)/i

Regex for capturing the numbers:

/([0-9]+)/

So you could have functions like:

function getAlpha($source) {
   preg_match("/([A-Z]+)/i", $source, $matches);
   return $matches[1];
}

function getNumeric($source) {
   preg_match("/([0-9]+)/", $source, $matches);
   return $matches[1];
}

And you would use it like this:

echo getAlpha("butterfly12"); //butterfly
echo getNumeric("butterfly12"); //12

EDIT

I now think I understand what you mean, perhaps these functions would work best for you:

function getAlpha($source) { //Gets whatever text is before a number.
    $alpha = "";
    if(preg_match("/^([A-Z]+)\d+/i", $source, $matches)) {
        $alpha = $matches[1];
    }
    return $alpha;
}

function getNumeric($source) { //Gets whatever number is after the text.
    $numeric = "";
    if(preg_match("/(\d+)$/", $source, $matches)) {
        $numeric = $matches[1];
    }
    return $numeric;
}