VB- Runtime Calc. of An Expression with User Defined Func.

[bomvoo]

I´m trying to make a program to calculate in run-time a numerical expression entered as a string. I am successful when the numerical expression contains only built-in VBA functions.

I would be grateful to get some information on how should I do to get an expression containing user defined functions to be calculated in runtime.

To clarify any doubts on the question, below are two examples. The first works, the second doesn´t, how should I do to get the second to work?

Thanks!

'**********************EXAMPLE 1 **********************
Sub working_example()

'setting input variable
X1 = 10
'string defining expression to be evaluated
f_of_x = "x^2+2*x+3"

Set sc = CreateObject("ScriptControl")
sc.Language = "VBScript"
sc.Reset
sc.ExecuteStatement ("x = " & X1) 'Execute statement for x variable = X1
result = sc.Eval(f_of_x) 'Evaluate it

'this works and give result=123

End Sub

'**********************EXAMPLE 2 **********************

Sub not_working_example()

'setting input variable
X1 = 10
'string defining expression to be evaluated - This does not work
f_of_x = "operation(x)"

Set sc = CreateObject("ScriptControl")
sc.Language = "VBScript"
sc.Reset
sc.ExecuteStatement ("x = " & X1) 'Execute statement for x variable = X1
result = sc.Eval(f_of_x) 'Evaluate it

'this does not work because f_of_x refers to a user defined function -operation-
'the question is how to include in a string expression a user defined function and
'get the expression calculated in run-time.
End Sub

************FUNCTION USED IN EXAMPLE 2 **********************

Function operation(x)

operation = x ^ 2 + 2 * x + 3

End Function

 

[Andrew Poulsom]

These worked for me:

Sub T1()
    f_of_x = "operation"
    x = 10
    result = Evaluate(f_of_x & "(" & x & ")")
    MsgBox result
End Sub

Sub T2()
    f_of_x = "operation()"
    x = 10
    result = Evaluate(Replace(f_of_x, "()", "(" & x & ")"))
    MsgBox result
End Sub