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

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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.
1+[[Basic Pascal Tutorial/Chapter 3/WHILE..DO|◄]] | [[Basic Pascal Tutorial/Contents|▲]] | [[Basic Pascal Tutorial/Chapter 3/FOR..IN|►]]
2+---|---|---
3+
4+REPEAT...UNTIL
45
5-It has the following syntax:
6+The repeat .. until construct is termed a _post_ -test loop, because the controlling condition is tested _after_ each iteration of the loop.
67
7-``` pascal
8+It has the following syntax:
9+```
810repeat
9- statement1;
10- // statement2;
11- // further statements...
12-until BooleanExpression;
11+ statement1;
12+ // statement2;
13+ // further statements...
14+ until BooleanExpression;
1315```
1416
15-A `repeat` loop encloses its executed statements, which means they do not need to be further enclosed in a begin ... end 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:
17+A `repeat` loop encloses its executed statements, which means they do not need to be further enclosed in a `begin ... end` 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`.
1818
19-``` pascal
19+For instance, the following `repeat` loop executes at least once:
20+```
2021repeat
21- WriteLn(Node.Text);
22- Node := GetNextNode;
23-until not Assigned(Node);
22+ WriteLn(Node.Text);
23+ Node := GetNextNode;
24+ until not Assigned(Node);
2425```
2526
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:
27+It assumes that Node is not Nil at the outset. If this assumption is incorrect, the code will fail, and the program may crash.
2928
30-``` pascal
29+A `while` loop is more defensive, since the needed check is performed before any loop statements are executed:
30+```
3131while Assigned(Node) do
32- begin
33- WriteLn(Node.Text);
34- Node := GetNextNode;
35- end;
32+ begin
33+ WriteLn(Node.Text);
34+ Node := GetNextNode;
35+ end;
3636```
3737
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.
38+Use a `repeat` loop when the looping statement(s) must execute at least once, whatever the initial value of the controlling Boolean condition.
4139
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:
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.
4341
44-``` pascal
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+```
4544repeat
46- statement1;
47- if Condition then
48- Break;
49- statement_that_might_affect_the_Condition;
50-until False;
45+ statement1;
46+ if Condition then
47+ Break;
48+ statement_that_might_affect_the_Condition;
49+ until False;
5150```
5251
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.
52+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.
5453
54+[[Basic Pascal Tutorial/Chapter 3/WHILE..DO|◄]] | [[Basic Pascal Tutorial/Contents|▲]] | [[Basic Pascal Tutorial/Chapter 3/FOR..IN|►]]
55+---|---|---
56+
5557---
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).*
58+*From the Free Pascal wiki, page "Basic Pascal Tutorial/Chapter 3/REPEAT..UNTIL", as the Internet Archive kept it on 2025-04-03, last changed on 2025-03-01. 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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