Break: what changed

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Title: Break

New		Line
1	+	The `break` (pseudo) [[Routine\|routine]] effectively destroys a [[Loops\|loop]]. Its primary application is to exit a loop prior its planned end.
2	+
3	+	`Break`, with its special meaning of abandoning a loop, can only be written within loops. It is not a reserved word¹, therefore you could shadow it, but access it by writing the fully qualified [[Identifier\|identifier]] [`system.break`](https://www.freepascal.org/docs-html/rtl/system/break.html) at any time, though.
4	+
5	+	## Collatz conjecture
6	+
7	+	Example: The following program tackles the [Collatz problem](https://en.wikipedia.org/wiki/Collatz_conjecture). The [[For\|for-loop]] in `collatzIterative` uses a `break`, a) to check for the terminating condition according to Collatz’ problem, b) to abort prior reaching the data type’s boundaries, and c) while still using the advantage of the `for`-construct (i. e. automatically [[Inc\|incrementing]] a variable within a specified range).
8	+
9	+	``` pascal
10	+	program collatz(input, output, stderr);
11	+
12	+	procedure collatzIterative(n: qword);
13	+	var
14	+	i: qword;
15	+	begin
16	+	for i := 0 to high(i) do
17	+	begin
18	+	writeLn('step ', i:20, ': ', n);
19	+
20	+	// Collatz conjecture: sequence ends with 1
21	+	if (n = 1) or (n > (high(n) / 3 - 1)) then
22	+	begin
23	+	// leave loop, as next value may get out of range
24	+	break;
25	+	end;
26	+
27	+	// n := ifThen(odd(n), 3 * n + 1, n div 2);
28	+	if odd(n) then
29	+	// n is odd
30	+	begin
31	+	n := 3 * n + 1;
32	+	end
33	+	// n is even
34	+	else
35	+	begin
36	+	n := n div 2;
37	+	end;
38	+	end;
39	+	end;
40	+
41	+	var
42	+	n: longword;
43	+	begin
44	+	readLn(n);
45	+
46	+	if n < 1 then
47	+	begin
48	+	writeLn(stderr, 'not a positive integer');
49	+	halt(1);
50	+	end;
51	+
52	+	collatzIterative(n);
53	+	end.
54	+	```
55	+
56	+	Choosing a `for`-loop in conjunction with a `break` is adequate, since the Collatz conjecture hypothesizes that the described function eventually ends in `1`, but does not tell for sure. Therefore – mathematically speaking – writing `while n <> 1 do` does not consider the circumstance, that the problem is an assumption, but would suggest it was determined to eventually result in `n = 1`.
57	+
58	+	## Other remarks
59	+
60	+	However, the usage of `break` is usually considered as bad style, since it “delegitimizes” the loop’s condition expression. You have to know a loop’s body contains a `break` to determine all abort conditions.
61	+
62	+	According to the [[GNU Pascal\|GPC]] manual, `break` is a [[Borland Pascal]] extension, whereas [[Mac Pascal]] has `leave`. [[FPC]], apart from [[Mode MacPas\|{$mode MacPas}]], only knows `break`, though.
63	+
64	+	## See also
65	+
66	+	- [`break`](https://www.freepascal.org/docs-html/rtl/system/break.html) in the `system` unit
67	+	- [[Exit\|exit]] to return from routines
68	+	- [[Continue\|continue]] to skip the rest of an iteration
69	+	- [[Goto\|goto]]
70	+
71	+	<small>
72	+
73	+	## sources
74	+
75	+	1
76	+	compare remarks in [the reference manual § “The `For..to`/`downto..do` statement”](https://www.freepascal.org/docs-html/ref/refsu58.html) and [§ “reserved words”](https://www.freepascal.org/docs-html/ref/refsu3.html)
77	+
78	+	</small>
79	+
80	+	---
81	+	From the Free Pascal wiki, page "Break", as it stood on 2020-11-20 after a change by Kai Burghardt, 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).
82	+	Category: Code

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