First steps with arrays in BBC BASIC for SDL

(Page's URL: bas6zero-first-steps-arrays.htm)

An array gives you some special variables.

When you've mastered the use of arrays, they will be a help to you.

Any time you use an array, you have to use the DIM keyword first.

If you put...

DIM Q$(2),A$(2)

... in a program, that gives you six variables you can then use...

Q$(0)
Q$(1)
Q$(2)
A$(0)
A$(1)
A$(2)

As usual, the $ at the "end" (well, the end before the bit in ()'s!) of the variable name means that this variable will be able to hold any character.

I've used arrays in the following geography test/ exercise....

REM bas6zero-test-by-array.bbc
REM vers 25 Feb 25
REM started  25 Feb 25

Q$(0)="France"
A$(0)="Paris"

Q$(1)="Italy"
A$(1)="Rome"

Q$(2)="India"
A$(2)="Delhi"

PRINT "Enter 000 at any time to finish"

REPEAT
    WhichQ%=RND(3)-1
    PRINT "What is the capital of ";Q$(WhichQ%)
    INPUT Ans$

    IF Ans$="000" THEN
       PRINT "Goodbye"
       WAIT (90)
       QUIT
    ENDIF

    IF Ans$=A$(WhichQ%) THEN PRINT "Right"
    IF Ans$<>A$(WhichQ%) THEN PRINT "Not right"

    PRINT

UNTIL FALSE

REM CHALLENGE: Add scoring, and a report of score at end.
REM CHALLENGE: Get program to provide right answer when user does not
REM CHALLENGE: Add code to let user have a second attempt
REM CHALLENGE: Make the user type the RIGHT answer if he/she had to be told

Much of that is unremarkable... but did you see the

A$(WhichQ%)

??? (It appears twice)

WhichQ% is an ordinary variable.

If WhichQ% holds, say, 1 in it when IF Ans$=A$(WhichQ%)... is executed, then, at that time, A$(WhichQ%) is as good as A$(1)

This is another of those things which is very cool... but which it may take you a while to see as very cool.

That's enough for now... we'll meet arrays again later. The next tutorial concentrating on how arrays can help you is bas6-introduction-to-arrays.htm.

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