Working with words

A string is a piece of text. Its name ends in $, it can be up to 255 characters long, and BASIC gives you five functions for cutting it up.

Gluing and measuring

+ joins two strings. LEN counts the characters:

A$ = "HELLO"
PRINT A$ + " THERE"
PRINT LEN(A$)

HELLO THERE
 5

OK

Go over 255 characters and you get ?STRING TOO LONG ERROR. It takes some doing.

Cutting it up

LEFT$(A$, 2)	the first 2 characters
RIGHT$(A$, 3)	the last 3
MID$(A$, 2, 3)	3 characters starting at the 2nd
MID$(A$, 3)	everything from the 3rd character on

PRINT LEFT$("HELLO", 2)
PRINT RIGHT$("HELLO", 3)
PRINT MID$("HELLO", 2, 3)

HE
LLO
ELL

OK

MID$ counts from 1, not from 0. Arrays count from zero and strings count from one, and no, nobody knows why.

Asking for more than there is doesn't hurt: LEFT$("ABC", 10) gives you ABC, and MID$("ABC", 4) gives you an empty string.

Letters and their numbers

Every character has a code. ASC gives you the code of a character and CHR$ gives you the character for a code:

PRINT ASC("A")
PRINT CHR$(65)

 65
A

OK

CHR$ is how you print a character you can't type — CHR$(34) is a double quote, which is otherwise impossible to get inside a string.

Numbers into text and back

STR$ turns a number into a string. VAL turns a string into a number:

PRINT "[" + STR$(42) + "]"
PRINT VAL("3.5"); VAL("12ABC"); VAL("ABC")

[ 42]
 3.5 12 0

OK

Two details in there. STR$(42) keeps the leading space that PRINT would have put in front of the number, so trim it with MID$(S$, 2) when you're building neat output. And VAL reads as far as it can and gives 0 when it can't read anything — it never errors, which makes it the safe way to accept a number from somebody.

Comparing them

The comparisons work in alphabetical order, and they're how you sort things:

PRINT "APPLE" < "BANANA"
PRINT "ABC" = "ABC"

-1
-1

OK

A worked example

10 F$ = "ADA"
20 L$ = "LOVELACE"
30 PRINT "NAME:   "; F$; " "; L$
40 PRINT "LETTERS:"; LEN(F$) + LEN(L$)
50 PRINT "INITIALS: "; LEFT$(F$, 1); "."; LEFT$(L$, 1); "."
60 PRINT "BACKWARDS: ";
70 FOR N = LEN(L$) TO 1 STEP -1
80 PRINT MID$(L$, N, 1);
90 NEXT N
100 PRINT

RUN
NAME:   ADA LOVELACE
LETTERS: 11
INITIALS: A.L.
BACKWARDS: ECALEVOL

OK

Lines 70 to 90 are the pattern to remember: a FOR loop counting down through a string, pulling out one character at a time with MID$(L$, N, 1). Reversing, searching and counting are all that loop with a different line 80.

Where the text goes

Strings live at the top of memory and grow downwards, while your program and variables grow up from the bottom. Every time you build a new string the old one is left behind as litter, and when the two meet, BASIC stops to sweep up. On a long string-heavy program you'll occasionally notice it pause for a moment: that is what's happening. What BASIC does with your memory has the map.

Next: keeping a list inside the program itself.