A declaration or declare may refer to any of the following:

  1. In programming, a declaration is a statement describing an identifier, such as the name of a variable or a function. Declarations are important because they inform the compiler or interpreter what the identifying word means, and how the identified thing should be used.

A declaration may be optional or required, depending on the programming language. For example, in the C programming language, all variables must be declared with a specific data type before they can be assigned a value.

Examples

Below are examples of declarations.

use strict;my $help;

The above perl statement declares a variable named $help. The dollar sign ($) indicates that the variable is a scalar. The special word my declares that $help has local lexical scope, meaning that outside the enclosing code block, the variable $help cannot be used.

Similarly, this Perl declaration:

Perl does not require that variables be declared unless strict is used. However, we always recommend using strict and declaring variable to help prevent problems with your code.

our $help;

…uses the special word our to declare that the scalar $help has global lexical scope. This declaration indicates the variable can be used anywhere in the program, and any part of the program can change the value of $help.

In some languages, a declaration and a value assignment can occur in a single statement. For example, in perl:

my $help = “Computer Hope”;

…declares a scalar variable $help with local scope, and assigns it the string value Computer Hope.

In the C programming language, this declaration:

int x;

…uses the special word int to declare that x is a variable of the integer data type. If the program tries to assign a non-integer value to x, the compiler returns an error. Similarly,

char str[30];

…declares an array named str that holds a maximum of 30 characters.

  1. When referring to a shell, declare is a builtin command of the Bash shell. See our declare command page for further information.
  • How to create a computer program.

Declarative programming, Programming terms