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.
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:
...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:
...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,