Remote-processing CAMBASIC Instrukcja Użytkownika Pobierz pdf (Strona 171)

Commands - 138

Strings ar e stored in tw o ways. A literal str ing (e. g., A$ = "string") is stor ed in the program line in

which it appears. Other strings that are formed as a result of string operations (like concatenation)

are stored star ting at the top of RAM and build down towar ds the numeric variables.

On power– up, you have 100 bytes of string space. You can change this with the CL EAR statement.

(Beneath the string area is the stack).

Thus, unused RA M extends from the top of the array space to the bottom of the stack.

EXAM PLE 1: 10 A = 1.1

20 B = VARPTR(A)

30 PRINT B ;

40 FOR X = 0 TO 3

50 PRINT PEEK(B+X) ;

60 NEXT : PRINT

RUN

17487 205 204 12 129

This example is for a simple num eric variable. The first number printed is the addr ess of the first

byte of the floating point representation of the number, or “1. 1”. This is the same as shown on the

previous page.

EXAM PLE 2: 10 H(0) = 1.1

20 Z = VARPTR(H(0))

30 PRINT Z

40 PRINT PEEK(Z) ; PEEK(Z+1) ; PEEK(Z+2) ; PEEK(Z+3)

RUN

17512

205 204 12 129

This routine retur ns the address of the first element of array H. The next e lement, if present, would

be at address 17004, the next at 17008, and so forth.

EXAM PLE 3: Addresses of array variables change each time a simple variable is assigned. For example:

10 T(0) = 0

20 PRINT VARPTR(T(0))

30 W = 0

40 PRINT VARPTR(T(0))

RUN

17484

17490

In this example, the variable W is first used after the array address was printed. Thus the array

address is shifted by the six bytes required for a simple variable.

EXAM PLE 4: 10 A$ = "Tuesday"

20 R = VARPTR(A$)

30 PRINT CHR$(PEEK(R))

In this case, new variables are declared after VARPTR returned the address. Unlike the array case,

1 2 ... 166 167 168 169 170 171 172 173 174 175 176 ... 207 208

Brak uwag

Remote-processing CAMBASIC Instrukcja Użytkownika Strona 171