How To Convert a Fraction to a Decimal Number

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This article provides a routine to convert a string that contains a fraction in the form "a," "a/b," or "a b/c" into a double precision floating-point number.

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Sometimes it is more convenient to input values as fractions instead of decimal numbers. The following routine converts a string containing a fraction to a decimal number:
  1. Create a new Visual Basic for Applications project and add the following code to a module:

    Sample Code

          Function Frac2Num(ByVal X As String) As Double
    Dim P As Integer, N As Double, Num As Double, Den As Double
    X = Trim$(X)
    P = InStr(X, "/")
    If P = 0 Then
    N = Val(X)
    Den = Val(Mid$(X, P + 1))
    If Den = 0 Then Error 11 ' Divide by zero
    X = Trim$(Left$(X, P - 1))
    P = InStr(X, " ")
    If P = 0 Then
    Num = Val(X)
    Num = Val(Mid$(X, P + 1))
    N = Val(Left$(X, P - 1))
    End If
    End If
    If Den <> 0 Then
    N = N + Num / Den
    End If
    Frac2Num = N
    End Function
  2. In the Debug/Immediate window, test:
    ? Frac2Num("5 3/4"), Frac2Num("2/8")
    Result: 5.75 0.25
Note: Numbers in the input string do not have to be whole numbers. They can contain decimal values and negative numbers.


For more information about getting help with Visual Basic for Applications, please see the following article in the Microsoft Knowledge Base:
163435 VBA: Programming Resources for Visual Basic for Applications

Id. de artículo: 185424 - Última revisión: 07/13/2009 - Revisión: 1