How to use the equivalent of indexof() with biginteger in VB.Net?

Question

I am trying to sum up the digits in a very large number. I have gotten the length of the number with
l = answer.bitLength() but I can't figure out how to increament through each digit using a For loop. Any ideas?

I'm using the java.math.biginteger .

Visual Studio 2005 Version 2.0

I should also add that I can't seem to use <> or any of the simple math options with the biginteger I'm using. If anyone could tell me how to use a different biginteger I would be more than willing to swap.

Dim answer As java.math.BigInteger
Dim sum As Integer = 0
Dim x As Integer
Dim i As Integer
'Sets value of answer equal to 1
answer = java.math.BigInteger.valueOf(1)

'gets 100!
For i = 1 To 100
answer = answer.multiply(java.math.BigInteger.valueOf(i))
Next

'gets length of answer
Dim l As Integer
l = answer.bitLength()

'Sums up digits in 100!
For x = 0 To l - 1
'Need to pull each character here to add them all up
Next

Final Solution for summing up the digits. Thanks to wageoghe.

Dim r As Integer
Dim s As Integer
s = 0
While (answer.compareTo(java.math.BigInteger.valueOf(0)) > 0)

r = answer.mod(java.math.BigInteger.valueOf(10)).ToString()
s = s + r
answer = answer.divide(java.math.BigInteger.valueOf(10))

End While

Answer 1

If you think of the number as a list of binary characters, then you could get the least significant hex digit by AND ing the number with 0xF . If you then shifted the number right by 4 bits ( >> 4 ), then you could get the next hex digit.

After you get all of the hex digits, you could sum them up and then convert them to decimal .

Answer 2

Something like this should work:

    Dim bi As New System.Numerics.BigInteger(12345)
    Dim c As Char
    Dim s As Long

    s = 0

    For Each c In bi.ToString()
        s = s + Integer.Parse(c.ToString())
    Next

Or this more conventional way using Mod and / (integer division)

    Dim bi As New System.Numerics.BigInteger(12345)
    Dim s As Long
    Dim r As Integer

    s = 0

    While bi <> 0
        r = bi Mod 10
        s = s + r
        bi = bi / 10
    End While

Answer 3

Another approach, is to do the following (this assumes that answer is positive):

int sum = 0;
while(answer > 0){
    sum += answer % 10;
    answer /= 10;
}