Microsoft open sources GWBASIC

[Norman Jaffe]

Yes, and on some machines, like the IBM 1800, small numeric constants are stored in a common location, to reduce the size of executable images. 
So, once you've changed 4 to 5, it means that all programs that get loaded will now use 5 when they meant 4. 
Usually the generated code has a way to refer to zero without using the common constant area, but not numbers like 1 or 2, so setting 1 or 2 to zero will have 'interesting' effects. 
Especially if the machine is controlling heavy equipment. 
[I bear witness to the result - been there, did that...] 

From: "cctalk" <cctalk at classiccmp.org> 
To: "cctalk" <cctalk at classiccmp.org> 
Sent: Monday, June 1, 2020 11:40:10 PM 
Subject: Re: Microsoft open sources GWBASIC 

On Mon, 1 Jun 2020 at 00:14, Eric Korpela via cctalk 
<cctalk at classiccmp.org> wrote: 

> C 
> C CHANGE THE VALUE OF 4 
> C 
> 
> CALL INC(4) 
> WRITE (*, 30) 4 
> 30 FORMAT ('2+2=',I4) 
> END 
> 
> SUBROUTINE INC(I) 
> I = I + 1 
> END 
> 
> -------- OUTPUT 
> 2+2= 5 

I had no idea, and I wrote a lot of FORTRAN for a few years. I just 
tested the above with the Fortran-77 compiler for my ND-100 mini, and 
yes, it prints 2+2= 5