Convert string from Base2 to Base4

Question

I wish to convert text to base 4 (AGCT), by first converting it to binary (I've done this bit) and then break it into 2 bit pairs.

can someone help me turn this into code using vb.net syntax?

if (length of binary String is an odd number) add a zero to the front (leftmost position) of the String. Create an empty String to add translated digits to. While the original String of binary is not empty { Translate the first two digits only of the binary String into a base-4 digit, and add this digit to the end (rightmost) index of the new String. After this, remove the same two digits from the binary string and repeat if it is not empty. }

in this context:

    Dim Base2Convert As String = ""
    For Each C As Char In Result.Text
        Dim s As String = System.Convert.ToString(AscW(C), 2).PadLeft(8, "0")
        Base2Convert &= s
    Next
    Result.Text = Base2Convert 

    Dim Base4Convert As String = ""
    For Each C As Char In Result.Text
        '//<ADD THE STATEMENT ABOVE AS CODE HERE>//
        Base4Convert &= s
    Next
    Result.Text = Base4Convert 

Answer 1

.NET does not support conversion to non-standard base, such as 4, so this will not work:

Dim base4number As String = Convert.ToString(base10number, 4)

From MSDN:

[...] base of the return value [...] must be 2, 8, 10, or 16.

But you can write your own conversion function, or take the existing one off the web:

Public Function IntToStringFast(value As Integer, baseChars As Char()) As String
  Dim i As Integer = 32
  Dim buffer(i - 1) As Char
  Dim targetBase As Integer = baseChars.Length

  Do
    buffer(System.Threading.Interlocked.Decrement(i)) =
      baseChars(value Mod targetBase)
    value = value \ targetBase
  Loop While value > 0

  Dim result As Char() = New Char(32 - i - 1) {}
  Array.Copy(buffer, i, result, 0, 32 - i)

  Return New String(result)
End Function

Used this answer. Converted with developer fusion from C# + minor adjustments. Example:

Dim base2number As String = "11110" 'Decimal 30
Dim base10number As Integer = Convert.ToInt32(base2number, 2)
Dim base4number As String = IntToStringFast(base10number, "0123") 
Console.WriteLine(base4number) 'outputs 132

Notice that you don't need base 2 there as an intermediate value, you can convert directly from base 10. If in doubt, whether it worked correctly or not, here is a useful resource:

• Number base converter

Answer 2

Converting the number to base first and then to base 4 doesn’t make a lot of sense, since directly converting to base 4 is the same algorithm anyway. In fact, representation of a number in any base requires the same general algorithm:

Public Shared Function Representation(number As Integer, digits As String) As String
    Dim result = ""
    Dim b = digits.Length

    Do
        result = digits(number Mod b) & result
        number \= b
    Loop While number > 0

    Return result
End Function

Now you can verify that Representation(i, decimal) does the same as i.ToString():

Dim decimalDigits = "0123456789"
For i = 0 To 30 Step 3
    Console.WriteLine("{0}, {1}", i.ToString(), Representation(i, decimalDigits))
Next

It’s worth noting that i.ToString() converts i to decimal base because this is the base we, humans, are mostly using. But there is nothing special about decimal, and in fact internally, i is not a decimal number: its representation in computer memory is binary.

For conversion to any other base, just pass a different set of digits to the method. In your case, that’d be "ACGT":

Console.WriteLine(Representation(i, "ACGT"))

Hexadecimal also works:

Console.WriteLine(Representation(i, "0123456789ABCDEF"))

And, just to repeat it because it’s such a nice mathematical property: so does any other base with at least two distinct digits.