116 lines
2.4 KiB
Markdown
116 lines
2.4 KiB
Markdown
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# 2. Getting started
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## The prompt
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Run `basic` with no arguments and you get a prompt:
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```
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$ ./build/basic
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READY
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```
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`READY` is printed whenever the interpreter is waiting for you, which is at startup
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and after a program stops.
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Anything you type **with a line number** is stored as part of a program. Anything you
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type **without** one runs immediately:
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```
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PRINT 2 + 2
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4
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READY
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```
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## Your first program
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```
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10 PRINT "WHAT IS YOUR NAME"
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20 INPUT "> " N$
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30 PRINT "HELLO, " + N$
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RUN
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```
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Type `LIST` to see it back, `RUN` to run it again, and `NEW` to throw it away.
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## Line numbers
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Lines are stored under their numbers and run in numeric order, so the gaps are what
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let you insert later:
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```
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10 PRINT "FIRST"
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30 PRINT "THIRD"
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20 PRINT "SECOND"
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LIST
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10 PRINT "FIRST"
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20 PRINT "SECOND"
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30 PRINT "THIRD"
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```
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Typing a line number with nothing after it deletes that line. `DELETE 20-40` removes a
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range, and `RENUMBER` tidies the whole program up — it rewrites every `GOTO` and
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`GOSUB` to match, so it will not break your branches.
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`AUTO 10` turns on automatic numbering so you do not have to type them; `AUTO 0` turns
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it off again.
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## Several statements on one line
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Statements are separated by colons:
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```
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10 A# = 1 : B# = 2 : PRINT A# + B#
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```
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There is one important limit: **block structures do not work inside a single line.**
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```
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10 FOR I# = 1 TO 3 : PRINT I# : NEXT I#
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```
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prints nothing at all. The loop body is skipped entirely, because the interpreter skips
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forward a *line* at a time looking for the `NEXT` and never finds one on the line it is
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already past. Write loops across several lines:
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```
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10 FOR I# = 1 TO 3
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20 PRINT I#
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30 NEXT I#
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```
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The same applies to `DO`/`LOOP`.
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## Running a file
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```sh
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$ ./build/basic program.bas
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```
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The file is read, stored, and run. It is exactly the same as typing the program in and
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saving yourself the trouble.
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You can also pipe a program in:
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```sh
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$ echo '10 PRINT "HI"
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RUN' | ./build/basic
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```
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## Saving and loading
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```
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DSAVE "myprogram.bas"
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DLOAD "myprogram.bas"
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```
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`SAVE` and `LOAD` are the same verbs under their other names. `VERIFY "myprogram.bas"`
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compares what is in memory against the file and prints `OK` if they match.
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## Stopping
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`QUIT` ends the interpreter. `STOP` stops a *program* and returns you to the prompt,
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where `CONT` resumes it from where it stopped. `END` also stops the program, but does
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not arm `CONT`.
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In the SDL build, closing the window stops the program too.
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