Default parameter: what changed

Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.

Title: Default parameter

New		Line
1	+	A default parameter also referred to as optional argument (or default argument) is a [[Function\|function]] or [[Procedure\|procedure]] parameter that has a default value provided to it. If the programmer does not supply a value for this parameter, the default value will be used. If the programmer does supply a value for the default parameter, the programmer-supplied value is used.
2	+
3	+	The programmer can extend an existing function or procedure by adding some parameters that have default value instead of writing an identical method with different parameters.
4	+
5	+	Beware: Once in a parameter list an optional parameter is defined, all following parameters have to be optional, too. A mandatory parameter must not have a later position than an optional parameter.
6	+
7	+	## Example `deadlineDay`
8	+
9	+	``` pascal
10	+	{$mode objfpc}
11	+
12	+	uses SysUtils, DateUtils;
13	+
14	+	function deadlineDay(day: integer; month: integer = 0): TDateTime;
15	+	var
16	+	n: TDateTime;
17	+	y, m, d: word;
18	+	begin
19	+	n := now();
20	+	DecodeDate(n, y, m, d);
21	+	if month = 0 then
22	+	begin
23	+	if d > day then
24	+	begin
25	+	n := IncMonth(n);
26	+	DecodeDate(n, y, m, d);
27	+	end;
28	+	end
29	+	else
30	+	begin
31	+	if month < m then
32	+	begin
33	+	n := IncYear(n);
34	+	end;
35	+	decodeDate(n, y, m, d);
36	+	m := month;
37	+	end;
38	+	d := day;
39	+	result := EncodeDate(y, m, d);
40	+	end;
41	+	```
42	+
43	+	Default parameter is used in place of the missing trailing parameter in a call
44	+
45	+	- in program call `deadlineDay(5)` effectively calls `deadlineDay(5, 0)`
46	+	- in program call `deadlineDay(5, 1)` does indeed call `deadlineDay(5, 1)`
47	+
48	+	---
49	+	From the Free Pascal wiki, page "Default parameter", as it stood on 2020-02-12 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).

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