Delphi Tutorial # 4

Identifier and Data Type

In this tutorial, we’re going to learn about Pascal Object - that serves as a basic for Delphi – such as data type, constant and variable. And you’ll be able to declare variables in a program and use operators in a statement.

Identifier

Identifier is used to declare constant, variable, unit, function, procedure etc. An identifier can be preceded by an underscore ( _ ), next character can be number, character string or underscore. The length of an identifier can be more than 255 characters, but only 255 first characters will be considered as an identifier. The rest characters will be ignored. Capital letter or small letter will be considered the same. And an identifier has to be non reserved word :

RESERVED WORD
and	array	as	asm
begin	case	class	const
constructor	destructor	dispinterface	div
do	downto	else	end
except	exports	file	finalization
finally	for	function	goto
if	implementation	in	inherited
initialization	inline	interface	is
label	library	mod	nil
not	object	of	or
out	packed	procedure	program
property	raise	record	repeat
resourcestring	set	shl	shr
string	then	threadvar	to
try	type	unit	until
used	var	while	with
xor	private	protected	public
published automated

Some examples of identifier are sum, salary, price, year etc. SALARY, Salary and salary are the same, because capital letter or small letter are considered the same.

Simple Data Type

Now we’ll learn some of data types in Pascal Object. Some of them categorize in simple data type. There are two simple data type : ordinal (integer, char, Boolean, string etc) and real.

Integer

Type	Range	Memory Size
Byte	0 to 255	1 byte
Word	0 to 65535	2 byte
ShortInt	-128 to 127	1 byte
SmallInt	-32768 to 32767	2 byte
Integer	-2147483648 to 2147483647	4 byte
Cardinal	0 to 2147483647	4 byte
LongInt	-2147483648 to 2147483647	4 byte

Char

Type	Memory Size	Saved Character
ANSIChar	1 byte	an ANSI Char
WideChar	2 byte	an Unicode Char
Char	1 byte	like an ANSIChar

Boolean

Type	Range	Memory Size
Boolean	one byte	1 byte
ByteBool	one byte	1 byte
Bool	one word	2 byte
WordBool	one word	2 byte
LongBool	double	4 byte

Real

String

Constant and Variable

Constant is a fixed value that is used in a program. To define a constant in a program, we use a reserved word const. Example :

  const

     discount = 0.1

or

  const

     discount : real = 0.1

discount is a constant which value is 0.1

But in a program, a value is not always fixed but it can be constantly changing. To handle this, we need variables. A variable can contain a value, and the value can be changed anytime. Before we can use a variable, it has to be declared first. Use reserved word var to declare a variable :

  Var

    Age : byte;

    Address : string;

    Salary : currency;

Age is a byte variable, its value can be 0 to 255. Address is a string variable. And Salary is a currency variable.

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