T.B.DBASIC operators
The following operators may be used as part of expressions. Arithmetic operators
The arithmetic operators take two numbers as operands.
+ add
multiply
A raise to the power
subtract divide
Relational operators
The relational operators can compare numbers, and return a logical value of FALSE=O and TRUE=-1.
< less than
<= less than or equal to <> not equal to
Logical operatorsequal to
> greater than
>= greater than or equal to
The logical operators operate on numeric or logical values. Boolean FALSE is taken as zero, TRUE as —1.
Indirection operators
The following operators allow the programmer to access memory directly (called PEEK in other versions of BASIC) or to alter the contents of specified memory locations (called POKE in other BASICs).
These operators should only be used by experienced programmers, since they give the programmer the capability of altering the operation of other activities in the Cambridge Z88 operating system; in general, only addresses within the region allocated by a BASIC DIM statement should be altered.
byte indirection word indirection string indirection
The usual way of using these operators is to allocate a vector using the DIM statement, and then manipulate elements of this vector with the indirection operators. For example,
DIM vec 15
allocates a vector of 16 bytes, and assigns its address to the variable vec. These bytes can be addressed as
Note that ?vec is an alternative way of writing vec ? 0. A typical manipulation might be
vec?l = vec?l + 1
Alternatively the vector could be addressed as 4 four-byte words:
Finally, the string indirection operator allows a string to be stored directly into an area of memory. For example:
$vec = "THE COMPUTER"
stores characters in the vector as follows:
The string can be accessed with the $ operator, so the following statement will print the string:
PRINT $vec
Individual characters can be accessed with the ? operator.
Order of precedence
The order of precedence of the operators is as follows:
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Group 7
unary minus brackets
logical NOT
A raise to the power
multiply divide
+ add subtract
less than
equal to
less than or equal to greater than
not equal to
greater than or equal to
AND Logical AND
OR Logical OR
FOR Logical Exclusive-OR
NOT
so, for example, A-B*CAD is equivalent to A-(B*(CAD)).