Difference between revisions of "*"
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{{*}} | {{*}} | ||
− | <div style="float: | + | <div style="float:right; margin: 0 25px 20px 0; padding:50px; font-size:500%; font-family: Georgia; background-color: #f9f9f9; border: 2px solid #777777;">*</div> |
− | The symbol '''''*'''' | + | == standard Pascal == |
+ | The symbol <syntaxhighlight lang="pascal" enclose="none">*</syntaxhighlight>, pronounced “asterisk”, is used in [[Pascal]] to | ||
+ | * indicate multiplication of numbers, or | ||
+ | * form the intersection of [[Set|sets]]. | ||
+ | |||
+ | <syntaxhighlight lang="pascal" highlight="13-15,17,18"> | ||
+ | program asteriskDemo(input, output, stderr); | ||
+ | |||
+ | type | ||
+ | day = (monday, tuesday, wednesday, | ||
+ | thursday, friday, saturday, sunday); | ||
+ | |||
+ | var | ||
+ | i: longint; | ||
+ | n: real; | ||
+ | m: set of day; | ||
+ | |||
+ | begin | ||
+ | // multiplication operator | ||
+ | i := 6 * 7; // i becomes 42 | ||
+ | n := 6.0 * 7.0; // n becomes 42.0 | ||
+ | |||
+ | // intersection operator | ||
+ | m := [saturday, sunday] * [sunday, monday]; | ||
+ | // m is now {sunday} | ||
+ | end. | ||
+ | </syntaxhighlight> | ||
+ | |||
+ | == exponentiation == | ||
+ | Furthermore, in [[FPC]] the exponentiation operator consisting of two consecutive asterisks <syntaxhighlight lang="pascal" inline>**</syntaxhighlight> exists. | ||
+ | However, it is only {{Doc|package=RTL|unit=system|identifier=.op-power-variant-ariant-ariant|text=defined for variants}} by the standard system unit, which requires a variant manager being installed. | ||
+ | In order to actually use it with integers, one can [[Operator overloading|define]] it on their own: | ||
+ | <syntaxhighlight lang="pascal" highlight="6-12,15"> | ||
+ | program exponentiation(input, output, stdErr); | ||
+ | |||
+ | // make operator overloading available | ||
+ | {$mode objFPC} | ||
+ | |||
+ | operator ** (const base: integer; const exponent: integer): integer; | ||
+ | begin | ||
+ | if base <> 0 then | ||
+ | begin | ||
+ | result := trunc(exp(ln(base) * exponent)); | ||
+ | end; | ||
+ | end; | ||
+ | |||
+ | begin | ||
+ | writeLn(2 ** 10); // will print 1024 | ||
+ | end. | ||
+ | </syntaxhighlight> | ||
+ | |||
+ | For readily available overloads, the {{Doc|package=RTL|unit=math|text=<syntaxhighlight lang="pascal" inline>math</syntaxhighlight>}} and {{Doc|package=RTL|unit=math|text=<syntaxhighlight lang="pascal" inline>matrix</syntaxhighlight> unit}} can be [[Uses|included]]. | ||
+ | |||
+ | == other appearances == | ||
+ | In Pascal's years of childhood computer systems did not necessarily knew the [[Comments|comment]] delimiting characters opening and closing curly brace <syntaxhighlight lang="pascal" enclose="none">{ }</syntaxhighlight>. | ||
+ | To make block comments available on such systems an alternative syntax, the bigramms <syntaxhighlight lang="pascal" enclose="none">(*</syntaxhighlight> and <syntaxhighlight lang="pascal" enclose="none">*)</syntaxhighlight> are allowed, too, but they can't be interchanged willynilly: | ||
+ | <syntaxhighlight lang="pascal" enclose="none">(*</syntaxhighlight> ''has'' to match a <syntaxhighlight lang="pascal" enclose="none">*)</syntaxhighlight>, and can ''not'' match a <syntaxhighlight lang="pascal" enclose="none">}</syntaxhighlight> even though it is closing a block comment, too. | ||
+ | |||
+ | Also, if C like operators were allowed by the compiler directive [[sCoperator|<syntaxhighlight lang="pascal" enclose="none">{$COperator on}</syntaxhighlight>]], the short syntax for <syntaxhighlight lang="pascal" enclose="none">i := i * n</syntaxhighlight> reads <syntaxhighlight lang="pascal" enclose="none">i *= n</syntaxhighlight>. | ||
+ | But by doing so, you leave the domain of Pascal. | ||
+ | Your code technically, mathematically speaking becomes wrong. | ||
+ | |||
+ | In [[ASCII]], the character code decimal <syntaxhighlight lang="pascal" enclose="none">42</syntaxhighlight> (or [[Hexadecimal|hexadecimal]] <syntaxhighlight lang="pascal" enclose="none">2A</syntaxhighlight>) is defined to be <syntaxhighlight lang="pascal" enclose="none">*</syntaxhighlight>. | ||
− | |||
{{Symbols}} | {{Symbols}} | ||
− | + | [[Category:Code]] | |
− |
Revision as of 22:43, 7 September 2019
│
English (en) │
suomi (fi) │
français (fr) │
русский (ru) │
standard Pascal
The symbol *
, pronounced “asterisk”, is used in Pascal to
- indicate multiplication of numbers, or
- form the intersection of sets.
program asteriskDemo(input, output, stderr);
type
day = (monday, tuesday, wednesday,
thursday, friday, saturday, sunday);
var
i: longint;
n: real;
m: set of day;
begin
// multiplication operator
i := 6 * 7; // i becomes 42
n := 6.0 * 7.0; // n becomes 42.0
// intersection operator
m := [saturday, sunday] * [sunday, monday];
// m is now {sunday}
end.
exponentiation
Furthermore, in FPC the exponentiation operator consisting of two consecutive asterisks **
exists.
However, it is only defined for variants by the standard system unit, which requires a variant manager being installed.
In order to actually use it with integers, one can define it on their own:
program exponentiation(input, output, stdErr);
// make operator overloading available
{$mode objFPC}
operator ** (const base: integer; const exponent: integer): integer;
begin
if base <> 0 then
begin
result := trunc(exp(ln(base) * exponent));
end;
end;
begin
writeLn(2 ** 10); // will print 1024
end.
For readily available overloads, the math
and matrix
unit can be included.
other appearances
In Pascal's years of childhood computer systems did not necessarily knew the comment delimiting characters opening and closing curly brace { }
.
To make block comments available on such systems an alternative syntax, the bigramms (*
and *)
are allowed, too, but they can't be interchanged willynilly:
(*
has to match a *)
, and can not match a }
even though it is closing a block comment, too.
Also, if C like operators were allowed by the compiler directive {$COperator on}
, the short syntax for i := i * n
reads i *= n
.
But by doing so, you leave the domain of Pascal.
Your code technically, mathematically speaking becomes wrong.
In ASCII, the character code decimal 42
(or hexadecimal 2A
) is defined to be *
.
single characters |
|
character pairs |
|