Basic Pascal Tutorial/Chapter 1/Variables and Data Types

1D - Variables and Data Types (author: Tao Yue, state: changed)

Variables are similar to constants, but their values can be changed as the program runs. Variables must first be declared in Pascal before they can be used:

var
  IdentifierList1 : DataType1;
  IdentifierList2 : DataType2;
  IdentifierList3 : DataType3;
  ...

IdentifierList is a series of identifiers, separated by commas (,). All identifiers in the list are declared as being of the same data type.

The basic data field data types in Pascal include:

• Integer
• Word
• LongInt
• Real
• Char
• Boolean

Standard Pascal does not make provision for the string data type, but most modern compilers do. Experienced Pascal programmers also use pointers for dynamic memory allocation, objects for object-oriented programming, and many others, but this gets you started.

More information on Pascal data types:

• The Integer data type can contain whole numbers. the size of an integer depends on the compiler and the processor. On PCs before the 80386, "integer" meant 16-bit whole numbers in the range from -32768 to 32767. This is the signed range that can be stored in a 16-bit word, and is a legacy of the era when 16-bit CPUs were common. For backward compatibility purposes, a 32-bit signed integer is a longint and can hold a much greater range of values, 2147483647 to -2147483648.
• The Word data type is a 16-bit unsigned integer, which has a range of 0 to 65535.
• The Real data type has a range from 3.4x10^-38 to 3.4x10^38, in addition to the same range on the negative side. Real values are stored inside the computer similarly to scientific notation, with a mantissa and exponent, with some complications. In Pascal, you can express real values in your code in either fixed-point notation or in scientific notation, with the character E separating the mantissa from the exponent. Thus, 452.13 is the same as 4.5213e2
• The Char data type holds characters. Be sure to enclose them in single quotes, like so: 'a' 'B' '+' Standard Pascal uses 8-bit characters, not 16-bits, so Unicode, which is used to represent all the world's language sets in one UNIfied CODE system, is not supported.
• The WideChar is a two-byte character (an element of a DBCS: Double Byte Character Set) and can hold a Unicode character. Note: some Unicode characters require two WideChars. See UTF-16.
• Free Pascal supports the Delphi implementation of the PChar data type. PChar is defined as a pointer to a Char type, but allows additional operations. The PChar type can be understood best as the Pascal equivalent of a C-style null-terminated string, i.e. a variable of type PChar is a pointer that points to an array of type Char, which is ended by a null-character (#0). Free Pascal supports initializing of PChar typed constants, or a direct assignment. For example, the following pieces of code are equivalent:

program one;  
var P : PChar;  
begin  
  P := 'This is a null-terminated string.';  
  WriteLn (P);  
end.

program two;  
const P : PChar = 'This is a null-terminated string.';  
begin  
  WriteLn (P);  
end.

• Free Pascal supports the String type as it is defined in Turbo Pascal: a sequence of characters with an optional size specification. It also supports AnsiStrings (with unlimited length) as in Delphi. And can be declared as:

variable_name : string;                    // if no length is given, it defaults to 255
variable_name : string[length];            // where:  1 < length <= 255

• The predefined type ShortString is defined as a string of size 255.
• AnsiStrings are strings that have no length limit. They are reference counted and are guaranteed to be null terminated. Internally, an ansistring is treated as a pointer: the actual content of the string is stored on the heap, as much memory as needed to store the string content is allocated.
• WideStrings (used to represent unicode character strings) are implemented in much the same way as ansistrings: reference counted, null-terminated arrays, only they are implemented as arrays of WideChars instead of regular Chars.
• The Boolean data type can have only two values: TRUE and FALSE

An example of declaring several variables is:

var
  Age, Year, Grade : integer;
  Circumference : real;
  LetterGrade : char;
  DidYouFail : boolean;

From the FPC manual

integer types

Free Pascal does automatic type conversion in expressions where different kinds of integer types are used.

real types

• Note that for Windows 64 bits and non-Intel targets Extended is an alias for Double.

boolean types

From the Free Pascal wiki, page "Basic Pascal Tutorial/Chapter 1/Variables and Data Types", as it stood on 2022-08-20 after a change by Kai Burghardt, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.