Binaryworld - DecToFrac - Converts a decimal number into a fraction ... [ VB -> Math ]

' Converts a decimal value into fractional parts as integers
' (based on the concept of Continued Fractions)

' Examples of usage:

' Call DeclToFrac(0.125, a, b) ' 1 and 8 are returned in a & b
' Call DecToFrac(5/40, a, b)   ' 1 and 8 are also returned
' Call DecToFrac(2/3, a, b)   ' 2 and 3 are returned

' Since more than one value needs to be returned, they are returned
' to variables which are passed by reference as arguments (Numerator
' and Denom) to the DecToFrac Sub procedure

Sub DecToFrac(DecimalNum As Double, Numerator As Long, Denom As Long)

' The BigNumber constant can be adjusted to handle larger fractional parts
Const BigNumber = 50000
Const SmallNumber = 1E-16

Dim Inverse As Double, FractionalPart As Double
Dim WholePart As Long, SwapTemp As Long

Inverse = 1 / DecimalNum
WholePart = Int(Inverse)
FractionalPart = Frac(Inverse)

If 1 / (FractionalPart + SmallNumber) < BigNumber Then
    ' Notice that DecToFrac is called recursively.
    Call DecToFrac(FractionalPart, Numerator, Denom)
    Numerator = Denom * WholePart + Numerator

    SwapTemp = Numerator
    Numerator = Denom
    Denom = SwapTemp
Else ' If 1 / (FractionalPart + SmallNumber) > BigNumber
    ' Recursion stops when the final value of FractionalPart is 0 or
    ' close enough. SmallNumber is added to prevent division by 0.
    Numerator = 1
    Denom = Int(Inverse)
End If
End Sub

' This function is used by DecToFrac and DecToProperFact

Function Frac(x As Double) As Double
  Frac = Abs(Abs(x) - Int(Abs(x)))
End Function

' This additional procedure handles "improper" fractions and returns
' them in mixed form (a b/c) when the numerator is larger than the denominator

Sub DecToProperFrac(x As Double, a As Long, b As Long, c As Long)
If x > 1 Then a = Int(x)
If Frac(x) <> 0 Then
   Call DecToFrac(Frac(x), b, c)
End If
End Sub