Conversion from binary to octal in php

Php program for Conversion from binary to octal. Here mentioned other language solution.

<?php
//  Php program for
//  Convert Binary number into Octal number
class Convert
{
	// Convert decimal number into octal
	function octal($number)
	{
		$result = 0;
		$multiplier = 1;
		$remainder = 0;
		while ($number != 0)
		{
			$remainder = $number % 8;
			$result = ($remainder * $multiplier) + $result;
			$multiplier *= 10;
			$number = (int)($number / 8);
		}
		return $result;
	}

	function binaryToOctal($num)
	{
		if (strlen($num) == 0)
		{
			// When empty binary number
			return;
		}
		// Some useful variable
		$flag = false;
		$decimalNo = 0;
		$counter = 0;
		$index = strlen($num) - 1;
		// We Assume that given binary number is valid
		// Here - indicates negative binary number
		// First convert binary to decimal
		// Example = 10111 => 23
		while ($index >= 0)
		{
			if ($num[$index] == '1')
			{
				$decimalNo += (1 << $counter);
			}
			else
			if ($num[$index] != '0')
			{
				if ($index == 0 && $num[$index] == '-')
				{
					// When get negative number
					$flag = true;
				}
				else
				{
					// Not a valid binary number
					return;
				}
			}
			$counter += 1;
			$index -= 1;
		}
		// When given number is 
		$output = $this->octal($decimalNo);
		if ($flag == true)
		{
			$output = -$output;
		}
		// Display given number
		echo "Binary : ".$num;
		// Display result
		echo " Octal : ".$output, "\n";
	}
}
$task = new Convert();
// Test Case
$task->binaryToOctal("1111");
$task->binaryToOctal("10111");
$task->binaryToOctal("101011");
$task->binaryToOctal("11011");
$task->binaryToOctal("-1000110");

Output

Binary : 1111 Octal : 17
Binary : 10111 Octal : 27
Binary : 101011 Octal : 53
Binary : 11011 Octal : 33
Binary : -1000110 Octal : -106