5

Using Program Units

The program unit is the source program with the program header. It has the following syntax:

<program unit> ::= <program heading> <declaration list> <program body>

Each program you write can have only one program unit. The program body is the first code that Pascal executes.

Using Module Units

A module unit is a source program that does not have a program header. It has the following syntax:

<module unit> ::= [ <module heading> ] <declaration list>

The module heading contains the reserved word module followed by an identifier:

<module heading> ::= [ 'module' <identifier> ';' ]

For example:

module sum;

This is a legal module heading. The module heading is optional.

Sharing Variables and Routines Across Multiple Units

Pascal supports three methods of sharing variables and routines between units:

•include files

•Multiple variable declarations

•extern/define variable declarations

These methods are not mutually exclusive; for example, you can declare a variable as either extern or define in an include file.

The following sections describe these methods.

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Pascal 4.0 User’s Guide