Difference between revisions of "Break"
(“break” is not a reserved word!; insert “real-world” example; add more content) |
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Example: | Example: | ||
| − | The following program | + | The following program tackles the [https://en.wikipedia.org/wiki/Collatz_conjecture Collatz problem]. |
The [[For|<syntaxhighlight lang="pascal" enclose="none">for</syntaxhighlight>-loop]] in <syntaxhighlight lang="pascal" enclose="none">collatzIterative</syntaxhighlight> uses a <syntaxhighlight lang="pascal" enclose="none">break</syntaxhighlight>, a) to abort prior reaching the data type's boundaries, and b) while still using the advantage of the <syntaxhighlight lang="pascal" enclose="none">for</syntaxhighlight>-construct, that is condition-checking and automatically [[Inc|incrementing]] a variable. | The [[For|<syntaxhighlight lang="pascal" enclose="none">for</syntaxhighlight>-loop]] in <syntaxhighlight lang="pascal" enclose="none">collatzIterative</syntaxhighlight> uses a <syntaxhighlight lang="pascal" enclose="none">break</syntaxhighlight>, a) to abort prior reaching the data type's boundaries, and b) while still using the advantage of the <syntaxhighlight lang="pascal" enclose="none">for</syntaxhighlight>-construct, that is condition-checking and automatically [[Inc|incrementing]] a variable. | ||
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* {{Doc|package=RTL|unit=system|identifier=break|text=<syntaxhighlight lang="pascal" enclose="none">break</syntaxhighlight>}} in the <syntaxhighlight lang="pascal" enclose="none">system</syntaxhighlight> unit | * {{Doc|package=RTL|unit=system|identifier=break|text=<syntaxhighlight lang="pascal" enclose="none">break</syntaxhighlight>}} in the <syntaxhighlight lang="pascal" enclose="none">system</syntaxhighlight> unit | ||
* [[Exit|<syntaxhighlight lang="pascal" enclose="none">exit</syntaxhighlight>]] to return from routines | * [[Exit|<syntaxhighlight lang="pascal" enclose="none">exit</syntaxhighlight>]] to return from routines | ||
| + | * [[Continue|<syntaxhighlight lang="pascal" enclose="none">continue</syntaxhighlight> to skip the rest of an iteration | ||
<small> | <small> | ||
Revision as of 02:13, 14 February 2018
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The break routine effectively destroys a loop.
Its primary application is to exit a loop prior its planned end.
break 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 identfier system.break at any time, though.
Example:
The following program tackles the Collatz problem.
The for-loop in collatzIterative uses a break, a) to abort prior reaching the data type's boundaries, and b) while still using the advantage of the for-construct, that is condition-checking and automatically incrementing a variable.
0program collatz(input, output, stderr);
1
2procedure collatzIterative(n: qword);
3var
4 i: qword;
5begin
6 for i := 0 to high(i) do
7 begin
8 // #9 is a tab character
9 writeLn(i, #9, n);
10
11 if (n = 1) or (n > (high(n) / 3 - 1)) then
12 begin
13 // leave loop, as next value may get out of range
14 break;
15 end;
16
17 if n mod 2 = 0 then
18 // n is even
19 begin
20 n := n div 2;
21 end
22 // n is odd
23 else
24 begin
25 n := 3 * n + 1;
26 end;
27 end;
28end;
29
30var
31 n: longword;
32begin
33 readLn(n);
34
35 if n < 1 then
36 begin
37 writeLn(stderr, 'not a positive integer');
38 halt(1);
39 end;
40
41 collatzIterative(n);
42end.
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 statement block contains a break to determine all abort conditions.
According to the GPC manual, break is a Borland Pascal extension, whereas Mac Pascal has leave.
see also
breakin thesystemunitexitto return from routines- [[Continue|
continueto skip the rest of an iteration
sources
- 1
- compare remarks in the reference manual § “The
For..to/downto..dostatement” and § “reserved words”
