Basic Pascal Tutorial/Chapter 3/REPEAT..UNTIL: what changed

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Title: Basic Pascal Tutorial/Chapter 3/REPEAT..UNTIL

New		Line
1	+	REPEAT...UNTIL
2	+
3	+	The repeat .. until construct is termed a post-test loop, because the controlling condition is tested after each iteration of the loop.
4	+
5	+	It has the following syntax:
6	+
7	+	``` pascal
8	+	repeat
9	+	statement1;
10	+	// statement2;
11	+	// further statements...
12	+	until BooleanExpression;
13	+	```
14	+
15	+	A `repeat` loop encloses its executed statements, which means they do not need to be further enclosed in a <tt>begin ... end<tt> block. Note that a repeat loop continues until its controlling Boolean expression is `True`; whereas the `while` loop continues until its Boolean expression is `False`.
16	+
17	+	For instance, the following `repeat` loop executes at least once:
18	+
19	+	``` pascal
20	+	repeat
21	+	WriteLn(Node.Text);
22	+	Node := GetNextNode;
23	+	until not Assigned(Node);
24	+	```
25	+
26	+	It assumes that Node is not Nil at the outset. If this assumption is incorrect, the code will fail, and the program may crash.
27	+
28	+	A `while` loop is more defensive, since the needed check is performed before any loop statements are executed:
29	+
30	+	``` pascal
31	+	while Assigned(Node) do
32	+	begin
33	+	WriteLn(Node.Text);
34	+	Node := GetNextNode;
35	+	end;
36	+	```
37	+
38	+	Use a `repeat` loop when the looping statement(s) must execute at least once, whatever the initial value of the controlling Boolean condition.
39	+
40	+	It is not difficult to inadvertently write a Boolean expression controlling a repeat loop that never becomes True. This gives rise to an infinite or endless loop, and causes the program to hang.
41	+
42	+	One programming style deliberately sets up an infinite loop, and inserts a `Break` or `Exit` instruction controlled by some condition evaluated in the middle of the loop to break out of the otherwise infinite loop:
43	+
44	+	``` pascal
45	+	repeat
46	+	statement1;
47	+	if Condition then
48	+	Break;
49	+	statement_that_might_affect_the_Condition;
50	+	until False;
51	+	```
52	+
53	+	Successful use of this style depends on Condition dependably becoming True, without exception, at some point. Otherwise you have built in an inescapable infinite loop.
54	+
55	+	---
56	+	From the Free Pascal wiki, page "Basic Pascal Tutorial/Chapter 3/REPEAT..UNTIL", as it stood on 2022-08-20 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).

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