PASCAL, Declaration Section, Routine Declaration
*Conan The Librarian (sorry for the slow response - running on an old VAX)
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/sys$common/syshlp/helplib.hlb PASCAL, Declaration Section, Routine Declaration *Conan The Librarian (sorry for the slow response - running on an old VAX) |
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The basic algorithm for a program can usually be divided into
relatively simple, repetitive tasks. In Pascal, you can code
each task separately as a routine; that is, as either a
procedure or a function. A procedure contains one or more
statements to be executed once the procedure is called. A
function contains one or more statements to be executed once the
function is called; in addition, functions return a single
value.
A routine call executes all statements in the body of the
declared routine. You must declare a routine before you can
call it. In addition, function calls return a single value.
Syntactically, procedure calls are statements, and function
calls are expressions. You can call routines in the executable
section of a program or in the body of another routine.
Syntax:
[[attribute-list]]
PROCEDURE routine-identifier [[formal-parameter-list]];
{ [[declaration-section]] BEGIN {statement};... END |
{EXTERN
EXTERNAL
FORTRAN
FORWARD} }
Syntax:
[[attribute-list]]
FUNCTION routine-identifier [[formal-parameter-list]]
: [[attribute-list]] result-type-id;
{ [[declaration-section]] BEGIN {statement};... END |
{EXTERN
EXTERNAL
FORTRAN
FORWARD} }
The 'attribute-list' is one or more optional identifiers that
provide additional information about the type-denoter.
The 'routine-identifier' is the name of the routine. If you use
the routine-identifier within the routine body (with the
exception of assigning a value to the routine-identifier of a
function), the result is a recursive call to the routine. The
routine-identifier of a procedure can be redeclared in the
procedure's declaration-section. The routine-identifier of a
function cannot be redeclared in the function's
declaration-section; however, it can be redeclared in any nested
routines within the function's declaration-section.
The 'formal-parameter-list' is a comma list of the routine's
formal parameters. A procedure can have as many as 255 formal
parameters; depending on the function return value, some
functions are limited to 254 formal parameters. Optionally, you
can specify a mechanism specifier and an attribute list for each
parameter.
The 'declaration-section' can include all sections except TO
BEGIN DO, TO END DO, and VALUE sections. Data specified in this
declaration section is local to the routine and to any nested
routines; you can redeclare identifiers that are declared in an
outer block. You cannot redeclare a formal parameter identifier
to be a local variable in the routine.
The 'statement' is any Compaq Pascal statement. In a function
executable section, there must be at least one statement of the
following form:
routine-identifier := result
The 'routine-identifier' is the name of the function.
The 'result' is a value of either an ordinal, real, structured,
or pointer type that VAX Pascal returns when function is called.
This value must be of the same type as the result-type-id, and
cannot be a file type or a structured type with a file
component.
'EXTERN', 'EXTERNAL', 'FORTRAN', and 'FORWARD' are predeclared
identifiers that direct Compaq Pascal to find the body of the
routine elsewhere. The EXTERN, EXTERNAL, and FORTRAN
identifiers declare routines that are independently compiled by
Compaq Pascal or that are written in other languages. In Compaq
Pascal, these identifiers are equivalent. Although not part of
the Pascal standard, many Pascal compilers only accept the
FORTRAN identifier for external routines actually written in
FORTRAN; if portability is a concern, you may wish to use
FORTRAN only for external FORTRAN routines.
The 'result-type-id' is the type specification of the function
return value. The function's result must be of this data type.
This type cannot be a file type or a structured type with a file
component.
Example:
PROCEDURE Read_Write( VAR A : INTEGER );
This declares a procedure, 'Read_Write', which takes one
variable parameter, 'A'.
Example:
FUNCTION Counter( VAR Instring, Outstring : VARYING[10] OF CHAR;
VAR Valid : Boolean ) : INTEGER;
This declares a function, 'Counter', which takes three variable
parameters, 'Instring', 'Outstring', and 'Valid' and returns an
INTEGER value.
Additional Information (explode) :
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