Conversion from binary to octal in kotlin

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

//  Kotlin program for
//  Convert Binary number into Octal number
class Convert {
    // Convert decimal number into octal
    fun octal(num : Int) : Int
    {
      	var number : Int = num;
        var result : Int = 0;
        var multiplier : Int = 1;
        var remainder : Int ;
        while (number != 0)
        {
            remainder = number % 8;
            result = (remainder * multiplier) + result;
            multiplier *= 10;
            number = number / 8;
        }
        return result;
    }
    fun binaryToOctal(num : String) : Unit
    {
        if (num.length == 0)
        {
            // When empty binary number
            return;
        }
        // Some useful variable
        var flag : Boolean = false;
        var decimalNo : Int = 0;
        var counter : Int = 0;
        var index : Int = num.length - 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.get(index) == '1')
            {
                decimalNo += (1 shl counter);
            }
            else
                if (num.get(index) != '0')
                {
                    if (index == 0 && num.get(index) == '-')
                    {
                        // When get negative number
                        flag = true;
                    }
                    else
                    {
                        // Not a valid binary number
                        return;
                    }
                }
            counter += 1;
            index -= 1;
        }
        // When given number is 
        var output : Int = this.octal(decimalNo);
        if (flag == true)
        {
            output = -output;
        }
        // Display given number
        print("Binary : " + num);
        // Display result
        println(" Octal : " + output);
    }
}
fun main(args : Array<String>) : Unit
    {
        val task : Convert = 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