TOPS-20 PASCAL Language Manual - Bitsavers

EXPRESSIONS
You can use parentheses in any expression to force a particular order
of evaluation, for example:
Expression:
Evaluates to:
8 * 5 DIV 2 ... 4 16
8 * 5 DIV (2 - 4) ····20
PASCAL evaluates the first expression according to the normal rules
for precedence. First, it multiplies 8 by 5 and divides the result
(40) by 2. Then, it subtracts 4 to get 16. The parentheses in the
second expression, however, force PASCAL to subtract before
multiplying or dividing. Hence, it subtracts 4 from 2, getting -2.
Then, it divides -2 into 40, with -20 as the result.
Parentheses can also help to clarify an expression.
could write the first example as follows:
For instance, you
«8 * 5) DIV 2) - 4
The parentheses eliminate any confusion about how the expression is to
be evaluated.
3.2 SCOPE OF IDENTIFIERS
The scope of an identifier is the part of the program in which you
have access to the identifier. In a PASCAL program, the scope of a
constant, type, variable, or subprogram identifier is the block in
which the identifier is declared. Figure 3-1 illustrates the scope of
identifiers declared at various levels.
Declarations in the main program block specify global identifiers,
which can be accessed in the main program and in all nested
subprograms. For example, A and B in Figure 3-1 are global
identifiers. They can be accessed from any level in the program.
Declarations in subprogram blocks specify local identifiers. You can
use a local identifier in the subprogram that contains its declaration
and in all its nested subprograms. For example, the identifiers C and
D are local to procedure Le~el lA and its nested subprograms Level 2A
and Level 3A. You can USE~ C and D i 11 any 0 f these subprog rams, but
not in the main program or in the subprograms Level_lB, Level_2B, and
Level 2C.
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