TOPS-20 PASCAL Language Manual - Bitsavers

PASCAL DATA TYPES
The base type can be any enumerated or predefined scalar type except
REAL. You can use a subrange type anywhere in the program where its
base type is legal. The rules for operations on a subrange are the
same as the rules for operations on its base type. A subrange and its
base type are compatible.
The use of subrange types can make a program clearer. For example,
integer values for the days of the year range from 1 to 365. Any
value outside this range is obviously incorrect. You could specify an
integer subrange for the days of the year as fo]lows:
VAF: Da~,~····Of···· y €·~a r J •• 366
By specifying a subrange, you indicate that the values of the variabJe
Day-Of-Year are restricted to the integers from 1 to 366.
Example
TYPE Months = CJan, Feb, Mar, Apr, Mas~ Jun,
Jul, Au~, Sep, Oct, Nov, Dec),
VAR Camp_Mos: Mas •• Oct;
Leaf_Mos: Sept.Nov;
First_Half: 'A' •• 'M';
We> l"'cf:
() •• t.l::.'.i5::~~;'
This example defines the variables Camp_Mos and Leaf_Mos as subranges
of the enumerated type Months. A Camp Mos value can be only May, Jun,
Jul, Aug, Sep, or Oct. A Leaf Mos val~e can be only Sep, Oct, or Nov.
The variable First Half is a subrange of the ASCII characters, with
possible values uppercase A through uppercase M. The variable Word is
a subrange of the integers from a to 05535.
2.2.2.3 The ORD Function - Each element of a scalar type (except the
REAL type) has a unique ordinal value, which indicates its order in a
list of elements of its type. The ORD function returns the ordinal
value as an integer, for example:
OR[lC '(~')
This expression returns 81, which is the ordinal value of uppercase Q
in the ASCII character set (see Appendix B). Note that the order of
the ASCII character set may not be what you expect. The numeric
characters are in numeric order, and the alphabetic characters are in
alphabetic order. All uppercase characters have lower ordina] values
than all lowercase characters, for example:
ORDC'Q') is less than ORDC'a') and
OF~D( 'A') is less than ORDC '7') but
ORDC'Z') is less than ORD('a')
You can use ORD on a value of an enumerated
are ordered starting at zero, for example:
type.
Enumerated
types
Of,[I C Tuef.)da~)
Assuming that Tuesday is a value of type Weekdays (which includes
values Monday, Tuesday, Wednesday, Thursday, and Friday),
expression returns the integer 1.
the
this
The ordinal value of an integer is the integer itself. For examp]e,
ORD(O) equals 0, ORD(23) equals 23, and ORD(-1984) equals -1984.
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