Typing it in

There are two ways to give the ACE an instruction, and the difference between them is one small thing: a number at the front.

Do it now

Type this and press Enter:

PRINT "GOOD MORNING"

GOOD MORNING

OK

It happened right away. This is immediate mode — no number in front, so BASIC does it and forgets it.

Do it later

Now type the same thing with a number in front:

10 PRINT "GOOD MORNING"

Nothing happens. That's right. A line with a number in front gets stored instead of run. You've written a program one line long. Type:

RUN

GOOD MORNING

OK

That's the whole distinction, and it never gets more complicated than that.

The numbers are the running order

Line numbers say what order things happen in, not what order you typed them. Type these three lines in this order:

30 PRINT "THIRD"
10 PRINT "FIRST"
20 PRINT "SECOND"

RUN
FIRST
SECOND
THIRD

OK

BASIC sorted them out. Count in tens, the way everyone does, and you leave yourself room to slip a line in later at 15.

Seeing what you've got

LIST shows the program:

LIST
10 PRINT "FIRST"
20 PRINT "SECOND"
30 PRINT "THIRD"

OK

LIST takes no arguments — it always shows the lot. (LIST 20 is a syntax error, which surprises people arriving from other BASICs.)

Changing a line

To change a line, type it again with the same number. The new one replaces the old:

20 PRINT "SECOND, BUT LOUDER"

To delete a line, type its number on its own and press Enter:

20

There is no line editor and no cursor to move around in a listing. Retyping a line is the way you edit, and it's why short lines are worth writing.

Get a line back the easy way

LIST, then read the line you want to fix off the screen and type it again with one word changed. On a terminal over the serial port you can copy and paste it, which is a good reason to hook a laptop up when you're writing something long.

Throwing it away

Three commands clear things out, and they're not the same:

Command	What goes	What stays
NEW	The program and the variables	Nothing
CLR	The variables	The program
RUN	The variables	The program

That last row catches people. RUN always starts with a clean slate of variables, so a value you set in immediate mode is gone the moment you RUN.

A = 99
RUN

…and A is back to 0.

Starting somewhere else

RUN on its own starts at the top. Give it a line number and it starts there:

RUN 20

Useful when the first half of a program has already done its job and you only want to see the rest.

More than one thing on a line

A colon joins statements together on a single line:

10 PRINT "TIME FOR" : PRINT "TWO THINGS"

Both run, left to right. It saves memory and typing, and it costs you readability, so use it where the two halves belong together.

Try this

Type this in, RUN it, then change line 20 to your own name and RUN it again:

10 PRINT "THIS PROGRAM BELONGS TO"
20 PRINT "ADA"
30 PRINT "AND IT WORKS"

Next: what a variable is, and what the machine can count to.