Why does this VBA code give -25 and not 25?

Question

This is a snippet from a book I am reading:

Sub VariantDemo()
  MyVar = True
  MyVar = MyVar * 100
  MyVar = MyVar / 4
  MyVar = "Answer: " & MyVar
  MsgBox MyVar
End Sub

In the answer box it says "Answer: -25"?, but why do we have the minus? When I calculate the value directly in Excel, the value is 25.

Not sure what the background context is but you are using `MyVar` to store Boolean, Integer, and String type values. I would avoid that if this is being used in some other context — urdearboy, Dec 30 '20 at 21:49
https://learn.microsoft.com/en-us/dotnet/visual-basic/language-reference/data-types/boolean-data-type#type-conversions — Marcucciboy2, Dec 30 '20 at 21:50
https://stackoverflow.com/questions/14462272/why-is-true-equal-to-1 — Matthew Kligerman, Dec 30 '20 at 21:51
Thanks, it is weird that Excel and VBA treats TRUE different. — arnis, Dec 30 '20 at 22:02
Does this answer your question? [Why is True equal to -1](https://stackoverflow.com/questions/14462272/why-is-true-equal-to-1) — John Alexiou, Dec 31 '20 at 03:59
@arnis, is this not the entire point of the demo function, given that the Sub is called VariantDemo? It's explaining the perils of not typing variables appropriately. — Rich Harding, Jan 03 '21 at 17:57

score 0 · Answer 1 · answered Dec 31 '20 at 04:12

In VBA is most other languages the numerical value of False is 0 and any other value is True. As a matter of convention and convenience, the value of True is cast as a signed integer as -1 and thus in your example -1*100/4 = -25.

For all signed integers a value filled with 1 bits, such as 11111111 equals -1. This is because of two's complement which maximizes storage for types where the first bit is the sign bit.

Why does this VBA code give -25 and not 25?

1 Answers1