Converting sting to variable

Hello everyone,

I am working on a vba code.

I have a function in terms of x, say (x)^2 + x.

I want to find values of this function for different values of x, say from 1 to 5.

For that I am using a 'for next' loop.

Example,

For x = 1 To 5

fx(x,1) = (x)^2 + x

Next x

But problem is that, this is not the only function. I want these values for any other functions of 'x', say cos(x), etc.

And I want this function to be given by a user as a sting in terms of 'x' either as an input in a cell or as input in inputbox and then I want to use this in 'for next' loop.

This is like converting a string to function with variable as 'x'.

Please help me. How to do this.

Thank you in advance.

I got this error while opening the file.

Also I could not find any macro.

I don't want to plot the values of the function.

I am assigning these values to arrays and doing further operations on them.

I think the question is clear now.

Carim

I opened your excel file, but is not helpful to me.

here is the actual code that I am working on

Sub ROMBERG_INTEGRATION()
Dim x As Double
Dim l As Double
Dim u As Double
Dim fx As Double
Dim fl As Double
Dim fu As Double
Dim i As Integer
Dim sum As Double
Dim pi As Double
Dim R_1(20, 1)
Dim R_2(20, 20)
Dim ii As Integer
pi = 3.14159265358979
l = 1.3 
u = 13.2 
fl = (l) ^ 1.3 + 10 ''' CHANGE FUNCTION HERE '''
fu = (u) ^ 1.3 + 10 ''' CHANGE FUNCTION HERE '''
sum = 0
For i = 0 To 20
 For x = l To u Step (u - l) / ((2) ^ i)
 fx = (x) ^ 1.3 + 10 ''' CHANGE FUNCTION HERE '''
 sum = sum + fx
 Next
 R_1(i, 1) = sum * 2
 sum = 0
Next
For ii = 0 To 19
 R_2(0, 0) = (fl + fu)
 R_2(ii, 0) = (u - l) / ((2) ^ (ii + 1)) * (fl + fu + R_1(ii - 0, 1))
Next

and the code continues..