Declaration (computer Programming)

Variables

In some programming languages an implicit declaration is provided the first time such a variable is encountered at compile time. In other languages such a usage is considered to be a fatal error, resulting in a diagnostic being issued. Some languages have started out with the implicit declaration behavior, but as they matured they provided an option to disable it (e.g. Perl's "use strict" or Visual Basic's "Option Explicit").

Examples of how various programming language implementations respond to undefined variables are given below. Each code example is followed by an error message (if any).

CLISP (GNU CLISP 2.35)

(setf y x)

*** - EVAL: variable X has no value

C# (.NET Framework)

static void Main { int y = x; }

Undefined variable x

C (GNU GCC 3.4)

int main { int y = x; return 0; }

foo.c: In function `main':
foo.c:2: error: `x' undeclared (first use in this function)
foo.c:2: error: (Each undeclared identifier is reported only once
foo.c:2: error: for each function it appears in.)

JavaScript (Mozilla Firefox 1.0)

y = x

 Error: x is not defined Source File: file:///c:/temp/foo.js

Standard ML (Standard ML of New Jersey v110.55)

val y = x;

stdIn:1.9 Error: unbound variable or constructor: x

MUMPS

Set Y = X

OCaml 3.08

let y = x;;

Unbound value x

Perl 5.8

my $y = $x;

(no error)

use strict; my $y = $x;

Global symbol "$x" requires explicit package name at foo.pl line 2.
Execution of foo.pl aborted due to compilation errors.

PHP 5

$y = $x;

(no error)

error_reporting(E_ALL); $y = $x;

PHP Notice: Undefined variable: x in foo.php on line 3

Python 2.4

x = y

Traceback (most recent call last): File "foo.py", line 1, in ? x = y
NameError: name 'y' is not defined

Ruby 1.8

y = x

NameError: undefined local variable or method `x' for main:Object
from (irb):1

VBScript (WSH 5.6)

Dim y y = x

(no error)

Option Explicit Dim y y = x

(3, 1) Microsoft VBScript runtime error: Variable is undefined: 'x'

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Famous quotes containing the word variables:

“The variables are surprisingly few.... One can whip or be whipped; one can eat excrement or quaff urine; mouth and private part can be meet in this or that commerce. After which there is the gray of morning and the sour knowledge that things have remained fairly generally the same since man first met goat and woman.”
—George Steiner (b. 1929)

“The variables of quantification, ‘something,’ ‘nothing,’ ‘everything,’ range over our whole ontology, whatever it may be; and we are convicted of a particular ontological presupposition if, and only if, the alleged presuppositum has to be reckoned among the entities over which our variables range in order to render one of our affirmations true.”
—Willard Van Orman Quine (b. 1908)

“Science is feasible when the variables are few and can be enumerated; when their combinations are distinct and clear. We are tending toward the condition of science and aspiring to do it. The artist works out his own formulas; the interest of science lies in the art of making science.”
—Paul Valéry (1871–1945)

Declaration (computer Programming) - Variables

Famous quotes containing the word variables: