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I'm working with legacy code and ran across something that I haven't been able to explain after several days of looking up tutorials and handbooks for GW Basic: a variable (P9%) is used in a comparison on line 530 (IF P9% <> 0) before the code would reach its definition on line 860. It's not a complex piece of code, only ~1200 lines total, so I am confident that I haven't missed any goto or gosub or anything that would reach 860 earlier than this comparison.

I am curious as to how this has been effecting the program as it runs. Most of my experience is with c++ where this sort of thing wouldn't compile, and if it did an unassigned variable could potentially contain anything that would fit, but I have no idea what kind of default assignment is given to a variable in Basic.

Tim
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It has been many years since I wrote much in gwbasic!

If I remember correctly the variable is assigned a zero value in that case. Gwbasic (and Qbasic I think) assigns a default value to all variables when first referenced, this is usually zero or the empty string for a string variable.

Interestingly when creating an array using the DIM statement, all the items in the array are also initialised this way.

Even with this mechanism it is usually better to initialise a variable, just to be clear what is happening.

Many programmers of the era writing for gwbasic omitted as much as they could to minimise the amount of memory used by the program instructions so they had more for other stuff. So that may be why it's not initialised.

user1855149
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