Quick start manual

5-6

Delphi Language Guide

Simple types

For more information about Unicode characters, see “About extended character sets”

on page 5-13 and “Working with null-terminated strings” on page 5-14.

Boolean types

The four predefined Boolean types are Boolean, ByteBool, WordBool, and LongBool.

Boolean is the preferred type. The others exist to provide compatibility with other

languages and operating system libraries.

A Boolean variable occupies one byte of memory, a ByteBool variable also occupies

one byte, a WordBool variable occupies two bytes (one word), and a LongBool variable

occupies four bytes (two words).

Boolean values are denoted by the predefined constants True and False. The

following relationships hold.

A value of type ByteBool, LongBool, or WordBool is considered True when its ordinality

is nonzero. If such a value appears in a context where a Boolean is expected, the

compiler automatically converts any value of nonzero ordinality to True.

The previous remarks refer to the ordinality of Boolean values, not to the values

themselves. In Delphi, Boolean expressions cannot be equated with integers or reals.

Hence, if X is an integer variable, the statement

if X then ...;

generates a compilation error. Casting the variable to a Boolean type is unreliable,

but each of the following alternatives will work.

if X <> 0 then ...; { use longer expression that returns Boolean value }

var OK: Boolean { use Boolean variable }

if X <> 0 then OK := True;

if OK then ...;

Enumerated types

An enumerated type defines an ordered set of values by simply listing identifiers that

denote these values. The values have no inherent meaning. To declare an

enumerated type, use the syntax

type typeName = (val

, ..., val

)

where typeName and each val are valid identifiers. For example, the declaration

type Suit = (Club, Diamond, Heart, Spade);

Boolean ByteBool, WordBool, LongBool

False < True False <> True

Ord(False) = 0 Ord(False) = 0

Ord(True) = 1 Ord(True) <> 0

Succ(False) = True Succ(False) = True

Pred(True) = False Pred(False) = True