Convert Trillion number to Binary - vb6

Question

In VB6, I am trying to convert a number to binary but when the number has 10 digits i am always getting an Overflow error.
What is the data type where i can store a trillion number?
This is the code which is working when the number has less that 10 digits.
Public Function DecimalToBinary(DecimalNum As Double) As _
String
Dim tmp As String
Dim n As Double
n = DecimalNum
tmp = Trim(Str(n Mod 2))
n = n \ 2
Do While n <> 0
tmp = Trim(Str(n Mod 2)) & tmp
n = n \ 2
Loop
DecimalToBinary = tmp
End Function

Answer 1

One of the problems you will encounter is that the Mod operator will not work with values larger than a Long (2,147,483,647). You can rewrite a Mod function as described in this answer: VBA equivalent to Excel's mod function:
' Divide the number by 2.
' Get the integer quotient for the next iteration.
' Get the remainder for the binary digit.
' Repeat the steps until the quotient is equal to 0.
Public Function DecimalToBinary(DecimalNum As Double) As String
Dim tmp As String
Dim n As Double
n = DecimalNum
Do While n <> 0
tmp = Remainder(n, 2) & tmp
n = Int(n / 2)
Loop
DecimalToBinary = tmp
End Function
Function Remainder(Dividend As Variant, Divisor As Variant) As Variant
Remainder = Dividend - Divisor * Int(Dividend / Divisor)
End Function
You can also rewrite your function to avoid Mod altogether:
Public Function DecimalToBinary2(DecimalNum As Double) As String
Dim tmp As String
Dim n As Double
Dim iCounter As Integer
Dim iBits As Integer
Dim dblMaxSize As Double
n = DecimalNum
iBits = 1
dblMaxSize = 1
' Get number of bits
Do While dblMaxSize <= n
dblMaxSize = dblMaxSize * 2
iBits = iBits + 1
Loop
' Move back down one bit
dblMaxSize = dblMaxSize / 2
iBits = iBits - 1
' Work back down bit by bit
For iCounter = iBits To 1 Step -1
If n - dblMaxSize >= 0 Then
tmp = tmp & "1"
n = n - dblMaxSize
Else
' This bit is too large
tmp = tmp & "0"
End If
dblMaxSize = dblMaxSize / 2
Next
DecimalToBinary2 = tmp
End Function
This function finds the bit that is larger than your number and works back down, bit by bit, figuring out if the value for each bit can be subtracted from your number. It's a pretty basic approach but it does the job.
For both functions, if you want to have your binary string in groups of 8 bits, you can use a function like this to pad your string:
Public Function ConvertToBytes(p_sBits As String)
Dim iLength As Integer
Dim iBytes As Integer
iLength = Len(p_sBits)
If iLength Mod 8 > 0 Then
iBytes = Int(iLength / 8) + 1
Else
iBytes = Int(iLength / 8)
End If
ConvertToBytes = Right("00000000" & p_sBits, iBytes * 8)
End Function