Identifiers in Pascal include the names of programs, names of variables, names of constants, and names of labels.

    In our first sample program, the name SampleProgram is an identifier that gives the name of the program.

program SimpleProgram (output);
begin
    writeln ('Hello World')
end.

    Pascal requires that all valid identifiers begin with a letter. After the first (initial) letter, the identifier may have any combination of letters and digits, but no other characters.

    Note that while the official Pascal standard forbids any characters other than digits and letters, many Pascal compilers do allow the underscore character (_) after the first character of an identifier.

    Pascal is case insensitive. That is, it makes no difference whether the letters or upper case or lower case. SAMPLEPROGRAM, sampleprogram, and SampleProgram are all the same identifier in pascal.

    Examples of valid Pascal identifiers:

    Lily    Frog32    Jump2Pad

    Examples of invalid (illegal, error) Pascal identifiers:

    9Lily    Kermit the Frog    Jump*over@me

    The first identifier (9Lily) is invalid because it starts with a number rather than a letter.

    The second identifier (Kermit the Frog) is invalid because it includes spaces.

    The third identifier (Jump*over@me) is invalid because it includes illegal characters (the * and the @) are neither letters nor digits.

    Note that you can not use any reserved word (such as program, begin, or end) as an identifier.

    While the official Pascal standard states that identifiers can be as long as you want (at least one character, but no upper limit), many pascal compilers have a shorter length used internally.

    Eight characters is a common limitation.

    GeorgeWashington
    GeorgeWashingtonCarver

    With an eight character limit, the Pascal compiler would accept both of these names, but would treat them as the same identifier, not as different identifiers, because they share the same first eight characters. This may seem silly, but this can cause headaches if you don’t know about this problem because it is easy to have two or more identifiers that start with the same eight characters.