Long Division

M.cs

public class M
{
    public static int[] DigitsOf(int value)
    {
        var numbers = new List<int>();
        for (; value > 0; value /= 10)
        {
            numbers.Add(value % 10);
        }
        return numbers.ToArray();
    }

    public static (int quotient, int remainder) Divide(int dividend, int divisor)
    {
        var digitsOfDividend = DigitsOf(dividend);

        var quotient = 0;

        var remainder = 0;

        for (var power = digitsOfDividend.Length - 1; power >= 0; power--)
        {
            var digit = digitsOfDividend[power];
            var number = remainder * 10 + digit;

            var howManyTimesDoesDivisorGoIntoNumber = number / divisor;

            quotient += howManyTimesDoesDivisorGoIntoNumber * (int) Math.Pow(10, power);

            var amount = howManyTimesDoesDivisorGoIntoNumber * divisor;

            remainder = number - amount;
        }

        return (quotient, remainder);
    }
}

UnitTest1.cs

public class UnitTest1
{
    [Fact]
    public void CanGetDigits()
    {
        Assert.Equal(new[] {5, 2, 4}, M.DigitsOf(425));
    }

    [Theory]
    [InlineData(8, 304, 38)]
    [InlineData(6, 72, 12)]
    [InlineData(2, 58, 29)]
    [InlineData(7, 161, 23)]
    [InlineData(2, 46, 23)]
    [InlineData(5, 85, 17)]
    [InlineData(7, 133, 19)]
    [InlineData(2, 66, 33)]
    [InlineData(7, 231, 33)]
    [InlineData(169, 78247, 463)]
    [InlineData(137, 18084, 132)]
    [InlineData(61, 21411, 351)]
    [InlineData(157, 43489, 277)]
    [InlineData(62, 17050, 275)]
    [InlineData(106, 20034, 189)]
    public void WholeNumberDivision(int divisor, int dividend, int expectedQuotient)
    {
        Assert.Equal(expectedQuotient, M.Divide(dividend, divisor).quotient);
    }

    [Theory]
    [InlineData(25, 435, 17, 10)]
    public void WithRemainderDivision(int divisor, int dividend, int expectedQuotient, int expectedRemainder)
    {
        var (quotient, remainder) = M.Divide(dividend, divisor);
        Assert.Equal(expectedQuotient, quotient);
        Assert.Equal(expectedRemainder, remainder);
    }
}