Sinclair ZX81 User Manual

Whereas B$ contains mere quote image characters (with code 192), A$ contains genuine string quote
characters (with code 11).
3. Run this program:
10
LET
A$="
LEN ""
ABDC
""
"
100
PRINT
A$;" = ";
VAL
A$
This will fail because
VAL
does not treat the quote image
""
as a string quote.
Insert some extra lines between 10 & 100 to replace the quote images in A$ by string quotes (which you
must call
CHR$
11), & try again.
Make the same modifications to the program in chapter , extercise 3, & experiment with it.
4. This subroutine deletes every occurance of the string "CARTHAGO" from A$.
1000
FOR
N=1
TO LEN
A$-7
1020
IF
A$(N
TO
N+7)="CARTHAGO"
THEN LET
A$(N TO N+7)="********"
1030
NEXT
N
1040
RETURN
Write a program that gives A$ various values (e.g. "DELENDA EST CARTHAGO.") & applies the
subroutine.

Sinclair ZX81 Specifications

General

Processor	Zilog Z80A
Processor Speed	3.25 MHz
ROM	8 KB
Input	Membrane keyboard
Storage	Cassette tape
Power Supply	9V DC
Dimensions	167 mm x 40 mm x 175 mm
Release Year	1981
Manufacturer	Sinclair Research
Weight	350 g
Operating System	Sinclair BASIC
RAM	1 KB
Ports	TV out, expansion port
Display	Television (RF modulator output)