ติดปัญหาเรื่อง การใส่จุดทศนิยมของตัวเลข เวลาแสดงผล ใน PHP [ช่วยหน่อยครับ]

$number = '105';
echo 'number: '.$number.'<br>';

$number_char_length = mb_strlen($number);
echo 'total char: ';
var_dump($number_char_length);
echo '<br>';

$number_sub_last_two = mb_substr($number, -2);
echo 'substr last two: ';
var_dump($number_sub_last_two);
echo '<br>';

$number_sub_before_last_two = mb_substr($number, 0, ($number_char_length-2));
echo 'number before substr last two: ';
var_dump($number_sub_before_last_two);
echo '<br>';

$number_custom_decimal_format = $number_sub_before_last_two.'.'.$number_sub_last_two;
echo 'custom decimal format: ';
var_dump($number_custom_decimal_format);
echo '<br>';

function intToDecimal($number = '', $decimal_place = 2, $force_float_val = true)
{
    // force number to be integer.
    $number = intval($number);
    // decimal must be integer and negative.
    $decimal_place = intval(-($decimal_place));

    $num_length = strlen($number);
    $num_last_two = substr($number, $decimal_place);
    $num_first_path = substr($number, 0, ($num_length-abs($decimal_place)));
    
    // make number as decimal (xxx.xx)
    $number_decimal = $num_first_path . '.' . $num_last_two;
    if ($force_float_val === true) {
        floatval($number_decimal);
    }
    
    // clear unwant value
    unset($num_first_path, $num_last_two, $num_length);
    
    return $number_decimal;
}// intToDecimal


echo '<h4>Test number to decimal</h4>';
echo intToDecimal('1234567890').'<br>';// 12345678.90
echo intToDecimal('90').'<br>';// .90
echo intToDecimal('3').'<br>';// .3
echo intToDecimal('-43289').'<br>';// -432.89

<script src="jquery-2.1.1.min.js"></script>
<input type=text id='test' data-val='' ><br>
<textarea id='text'  rows="20"></textarea>
<script>
Number.prototype.format = function(n, x) {
    var re = '\\d(?=(\\d{' + (x || 3) + '})+' + (n > 0 ? '\\.' : '$') + ')';
    return this.toFixed(Math.max(0, ~~n)).replace(new RegExp(re, 'g'), '$&,');
};
$(document).ready(function(e){
    $('#test').keydown(function(e){
		var z = parseInt('0'+$('#test').data('val'));
		var y = e.which; // or e.keyCode;
		if(y>95 && y<106) y += 48 - 96;
		$('#text').val( $('#text').val() +y + '==' + x +"\n" );
		switch( y ){
		case 8: //backspace
			z = Math.floor(z / 10);
			break;
		default:
			var x = String.fromCharCode( y );
			if(x<'0' || x>'9'){  // เฉพาะตัวเลข
				$('#text').val( $('#text').val() +"clear\n" );
			}else {
				z = (z * 10) + parseInt(x);
			}
		}
		$('#test').val( (z / 100).format(2) ).data('val', z);
		$('#text').val( $('#text').val() + z + "\n" );
		return false; 
	});
});
</script>