How to convert base 10 negative number to base 8 conversion without using Convert.To() method?

Question

How can i represent decimal negative number in octal without using Convert.To() method?

public static string GetOctal(int number)
{     
   int base = 8;    
}

So for example :

-3 (base 10) = 37777777775 (base 8)

But what algorithm should i use to get this result?

The are test cases for my task:

        [TestCase(-3, 8, ExpectedResult = "37777777775")]
        [TestCase(-127, 8, ExpectedResult = "37777777601")]
        [TestCase(-675432, 8, ExpectedResult = "37775330630")]
        [TestCase(-1908345, 8, ExpectedResult = "37770560607")]
        [TestCase(int.MinValue, 8, ExpectedResult = "20000000000")]
        [TestCase(-3, 16, ExpectedResult = "FFFFFFFD")]
        [TestCase(-127, 16, ExpectedResult = "FFFFFF81")]
        [TestCase(-675432, 16, ExpectedResult = "FFF5B198")]
        [TestCase(-1908345, 16, ExpectedResult = "FFE2E187")]
        [TestCase(int.MinValue, 16, ExpectedResult = "80000000")]
        [TestCase(1908345, 10, ExpectedResult = "1908345")]
        [TestCase(int.MaxValue, 10, ExpectedResult = "2147483647")]
        public string GetRadix_Tests(int number, int radix) => number.GetRadix(radix);

Answer 1

You can always go the source code of the Convert class at source.dot.net here and follow ParseNumber's IntToString method:

public static string IntToString(int n, int radix, int width, char paddingChar, int flags)
{
    Span<char> buffer = stackalloc char[66]; // Longest possible string length for an integer in binary notation with prefix

    if (radix < MinRadix || radix > MaxRadix)
        throw new ArgumentException(SR.Arg_InvalidBase, nameof(radix));

    // If the number is negative, make it positive and remember the sign.
    // If the number is MIN_VALUE, this will still be negative, so we'll have to
    // special case this later.
    bool isNegative = false;
    uint l;
    if (n < 0)
    {
        isNegative = true;
    (...)