HP 3000 Manuals HP 3000 Manuals
Data Items - Classes and Categories
Data items in a COBOL program are specified and referenced very
precisely. The various restrictions governing data items are outlined
below.
Classes of Data Items
COBOL has three general classes of data items:
* Alphabetic, which can contain letters (A through Z) or spaces, in
any combination.
* Numeric, which can contain digits (0 through 9) in any
combination, optionally including an operational sign. This is
the only class of data item that can be used in arithmetic
operations.
* Alphanumeric, which can contain any characters from the ASCII
character set, in any combination.
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NOTE For complete compatibility with all ANSI COBOL compilers,
use only members of the COBOL character set.
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Categories of Data Items
The three classes of data items are subdivided into five categories:
* Alphabetic, which is synonymous with the alphabetic class.
* Numeric, which is synonymous with the numeric class.
* Alphanumeric, which can contain any characters from the ASCII
character set in any combination, not edited by a PICTURE clause.
* Alphanumeric-edited, which can contain any characters from the
ASCII character set in any combination, plus editing symbols
supplied by a PICTURE clause.
* Numeric-edited, which can contain any digits (0 through 9), plus
editing symbols supplied by a PICTURE clause.
NOTE More precise definitions of these categories appear under the
description of the PICTURE clause in Chapter 7 .
These classes and categories are independent of the external or internal
storage formats of the data items. The relation of classes to categories
are summarized in Table 4-1 . For alphabetic and numeric data items,
the classes and categories are synonymous. For alphanumeric data items,
the relation of class to category depends on the level (group or
elementary) of the data item within the record structure. Every
elementary item (except an index data item) belongs to one of these
classes and categories. During program execution, every group item is
treated as an alphanumeric item regardless of the class of the elementary
items subordinate to that group item.
Table 4-1. Data Item Classes and Categories
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- Level of Item - Class - Category -
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- Elementary - Alphabetic - Alphabetic -
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- - Numeric - Numeric -
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- - Alphanumeric - Numeric Edited -
- - - Alphanumeric Edited -
- - - Alphanumeric -
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- Group - Alphanumeric - Alphabetic -
- - - Numeric -
- - - Numeric Edited -
- - - Alphanumeric Edited -
- - - Alphanumeric -
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