Declaration

Updated: 09/15/2017 by Computer Hope

In programming, a declaration is a statement that describes 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.

Below are some examples of declarations.

Examples

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:

our $help;

...uses the special word our to declare that the scalar $help has global lexical scope. This declaration means that 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 will return an error. Similarly,

char str[30];

...declares an array named str which can hold a maximum of 30 characters.

Programming terms