Difference between revisions of "*"

From Free Pascal wiki
m (exponentiation: insert link to operator overloading)
(exponentiation: review example)
 
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== exponentiation ==
 
== exponentiation ==
Furthermore, in [[FPC]] the exponentiation operator consisting of two consecutive asterisks <syntaxhighlight lang="pascal" enclose="none">**</syntaxhighlight> exists.
+
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.
 
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:
 
In order to actually use it with integers, one can [[Operator overloading|define]] it on their own:
<syntaxhighlight lang="pascal" highlight="6-9,12">
+
<syntaxhighlight lang="pascal" highlight="6-12,15">
program exponentiation(input, output, stderr);
+
program exponentiation(input, output, stdErr);
  
 
// make operator overloading available
 
// make operator overloading available
{$mode objfpc}
+
{$mode objFPC}
  
 
operator ** (const base: integer; const exponent: integer): integer;
 
operator ** (const base: integer; const exponent: integer): integer;
 
begin
 
begin
result := trunc(exp(ln(base) * exponent));
+
if base <> 0 then
 +
begin
 +
result := trunc(exp(ln(base) * exponent));
 +
end;
 
end;
 
end;
  
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</syntaxhighlight>
 
</syntaxhighlight>
  
For readily available overloads, the {{Doc|package=RTL|unit=math|text=<syntaxhighlight lang="pascal" enclose="none">math</syntaxhighlight>}} and {{Doc|package=RTL|unit=math|text=<syntaxhighlight lang="pascal" enclose="none">matrix</syntaxhighlight> unit}} can be [[Uses|included]].
+
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 ==
 
== other appearances ==

Latest revision as of 22:43, 7 September 2019

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*

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 *.


navigation bar: topic: Pascal symbols
single characters

+ (plus)  •  - (minus)  •  * (asterisk)  •  / (slash)
= (equal)  •  > (greater than)  •  < (less than)
. (period)  •  : (colon)  •  ; (semi colon)
^ (hat)  •  @ (at)
$ (dollar sign)  •  & (ampersand)  •  # (hash)
' (single quote)

character pairs

<> (not equal)  •  <= (less than or equal)  •  := (becomes)  •  >= (greater than or equal)

 •  >< (symmetric difference)  •  // (double slash)