Changing the contents of a cell in a range, controlled from a separate cell

In cell B1 = 60 (number)
The range A1:A100 is filled with 0
I need a formula or function which changes the contents of A60 into e.g. 1
(the argument 60 in A60 comes from B1)
When the contents of cell B1 is changed from 60 to let us say 30 then A60 must be 0 again and A30 must be 1.

Does a formula or VBA code exist which can do this for me?

your help will be appreciated

Gerhard

Here is one approach. Right-click on the worksheet tab, View Code and paste this in. It will update when you change B1:

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Your code works perfectly when I change the contents of B1 manually.
However in cell B1 is a formula which gets its information to change the value from a differt cell.
I tested by entering in cell B1 the formula =+C1
When I change the contents of C1, cell B1 changes accordingly but nothing happens to range A1:A100. Can you advise an alternative approach please?