Difference between revisions of "Real"
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<syntaxhighlight lang="pascal" inline>real</syntaxhighlight> is a [[Standard type|standard type]] of the [[Pascal]] programming language. | <syntaxhighlight lang="pascal" inline>real</syntaxhighlight> is a [[Standard type|standard type]] of the [[Pascal]] programming language. | ||
+ | Despite its name, the data type <syntaxhighlight lang="pascal" inline>real</syntaxhighlight> only provides a “reasonable approximation” of ℝ, the set of real numbers. | ||
+ | For example the real number <math>\sqrt{2}</math> may have the <syntaxhighlight lang="pascal" inline>real</syntaxhighlight> value of <syntaxhighlight lang="pascal" inline>1.4</syntaxhighlight> in Pascal. | ||
== usage == | == usage == | ||
Line 12: | Line 14: | ||
begin | begin | ||
− | r := 0.; | + | r := 0.0; { r becomes zero } |
writeLn(r, ' ', r:8:4); | writeLn(r, ' ', r:8:4); | ||
− | r := 1e2; | + | r := 1e2; { r becomes 1*(10^2) [a hundred] } |
writeLn(r, ' ', r:8:4); | writeLn(r, ' ', r:8:4); | ||
− | r := r / r; | + | r := r / r; { r becomes one } |
writeLn(r, ' ', r:8:4); | writeLn(r, ' ', r:8:4); | ||
end. | end. | ||
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== alternatives == | == alternatives == | ||
− | Instead of specifying <syntaxhighlight lang="pascal" inline>real</syntaxhighlight> in your code, write {{Doc|package=RTL|unit=system|identifier=valreal|text=<syntaxhighlight lang="pascal" inline>ValReal</syntaxhighlight>}}, a type alias | + | Instead of specifying <syntaxhighlight lang="pascal" inline>real</syntaxhighlight> in your code, write {{Doc|package=RTL|unit=system|identifier=valreal|text=<syntaxhighlight lang="pascal" inline>ValReal</syntaxhighlight>}}, a type alias {{gitlab|repository|FPC|release_3_2_0/rtl/inc/systemh.inc#L123-332|defined by}} the [[System unit]]. |
It automatically maps to the largest available floating point type available: <syntaxhighlight lang="pascal" inline>single</syntaxhighlight>, <syntaxhighlight lang="pascal" inline>double</syntaxhighlight> or <syntaxhighlight lang="pascal" inline>extended</syntaxhighlight>. | It automatically maps to the largest available floating point type available: <syntaxhighlight lang="pascal" inline>single</syntaxhighlight>, <syntaxhighlight lang="pascal" inline>double</syntaxhighlight> or <syntaxhighlight lang="pascal" inline>extended</syntaxhighlight>. | ||
+ | |||
+ | == see also == | ||
+ | * [[Fractions]] | ||
{{Data types}} | {{Data types}} |
Latest revision as of 16:32, 25 January 2023
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real
is a standard type of the Pascal programming language.
Despite its name, the data type real
only provides a “reasonable approximation” of ℝ, the set of real numbers.
For example the real number [math]\displaystyle{ \sqrt{2} }[/math] may have the real
value of 1.4
in Pascal.
usage
Floating-point literals can be assigned to real
variables.
1program realDemo(input, output, stderr);
2
3var
4 r: real;
5
6begin
7 r := 0.0; { r becomes zero }
8 writeLn(r, ' ', r:8:4);
9
10 r := 1e2; { r becomes 1*(10^2) [a hundred] }
11 writeLn(r, ' ', r:8:4);
12
13 r := r / r; { r becomes one }
14 writeLn(r, ' ', r:8:4);
15end.
real
, like all floating-point types, supports /
division operator, while integer types support div
-operator.
internal representation
The internal representation of the type real
(i.e. number of bytes and byte ordering) and the resulting range and precision are platform dependent.
Quote from the “FreePascal Programmer's Manual” (Chapter 8.2.5 Floating point types):
Contrary to Turbo Pascal, where the
real
type had a special internal format, under Free Pascal thereal
type simply maps to one of the other real types. It maps to thedouble
type on processors which support floating point operations, while it maps to thesingle
type on processors which do not support floating point operations in hardware.
alternatives
Instead of specifying real
in your code, write ValReal
, a type alias defined by the System unit.
It automatically maps to the largest available floating point type available: single
, double
or extended
.
see also
simple data types |
|
---|---|
complex data types |