COBOL Programming Course

Peter Kitson

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Categories of COBOL data

Variables

A data-name or identifier is the name used to identify the area of memory reserved for a variable. A variable is a named location in memory into which a program can put data, and from which it can retrieve data.

Every variable used in a COBOL program must be described in the DATA DIVISION. 

Variable Data Types

Some languages like Modula-2,Pascal or Ada are described as being strongly typed. In these languages there are a large number of different data types and the distinction between them is rigorously enforced by the compiler. For instance, the compiler will reject a statement that attempts to assign character value to an integer data item.

In COBOL, there are really only three data types -

- numeric
- alphanumeric (text/string)
- alphabetic

The distinction between these data types is a little blurred and only weakly enforced by the compiler. For instance, it is perfectly possible to assign a non-numeric value to a data item that has been declared to be numeric.

The problem with this lax approach to data typing is that, since COBOL programs crash (halt unexpectedly) if they attempt to do computations on items that contain non-numeric data, it is up to the programmer to make sure this never happens.

COBOL programmers must make sure that non-numeric data is never assigned to numeric items intended for use in calculations. Programmers who use strongly typed languages don't need this level of discipline because the compiler ensures that a variable of a particular types can only be assigned appropriate values.

Literals

A literal is a data-item that consists only of the data-item value itself. It cannot be referred to by a name. By definition, literals are constant data-items.

There are two types of literal -

* String/Alphanumeric Literals
* Numeric Literals