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Comment by allenu | Hacker News Reader

It gets run in the correct order. Think of each line as a command that stores the instruction immediately at that line number. You could actually "re-type" a line later by reusing the same line number but replacing it with new contents.

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"Correct" order is ambiguous to someone asking that question in the first place.

It sounds like he's saying the "line number" is just the index to a tokenized list (i.e. line 15 is at `lines[15]') where unused lines are just nops. So my "program" would be tokenized and the lines stored like:

    char** lines = malloc(...);
    lines[10] = &line1;
    lines[30] = &line2;
    lines[20] = &line3;

Then when executing, it starts at `lines[0]', sees nops, gets to `lines[10]' and runs it, sees more nops, gets to `lines[20]' and jumps to `lines[10]'. All the while ignoring `lines[21]' and up.

Usually in 8-bit BASICs the lines would be stored consecutively (not in separate malloced segments) with each line starting with its line number. Yes, this meant that GOTO required a search. Memory was a really central design constraint on these systems. I don't know how closely MS's BASICA on the PC followed this model, but the PC's starting configuration had 16k bytes of RAM.

Here's a description of the file format used by BBC Basic:

http://xania.org/200711/bbc-basic-v-format

That's Basic V, which was the variant used on the ARM-based Archimedes, but it's the same file format as the 6502 machine Basics.

Note that the line numbers used by GOTO and GOSUB were specially flagged --- this was so the RENUMBER command could find them. It also meant that computed gotos weren't renumbered...

(Of course, BBC Basic had proper named procedures and functions with local variables, but all self-respecting Basics had to support GOTO and GOSUB.)

Spot on - so line 30 would never get executed on that code, and a series of '1's will get printed, in an endless loop, until stopped with a Ctrl-C.

What is "correct order"? You forgot to answer the actual question.

Sorry, it was ambiguous. I assumed the writer of the original code intended to execute them in the order of the line numbers and that was the "correct order". Otherwise, the line numbers are meaningless.

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