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: <delphi> var
IdentifierList1 : DataType1; IdentifierList2 : DataType2; IdentifierList3 : DataType3; ...
</delphi> 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 types in Pascal include:
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 integers 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.
- The real data type has a range from 3.4x10-38 to 3.4x1038, 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 boolean data type can have only two values: TRUE and FALSE
An example of declaring several variables is: <delphi> var
age, year, grade : integer; circumference : real; LetterGrade : char; DidYouFail : Boolean;
From the FPC manual
|Byte||0 .. 255||1|
|Shortint||-128 .. 127||1|
|Smallint||-32768 .. 32767||2|
|Word||0 .. 65535||2|
|Integer||smallint or longint||2 or 4|
|Longint||-2147483648 .. 2147483647||4|
|Int64||-9223372036854775808 .. 9223372036854775807||8|
|QWord||0 .. 18446744073709551615||8|
Free Pascal does automatic type conversion in expressions where different kinds of integer types are used.
|Real||platform dependant||???||4 or 8|
|Single||1.5E-45 .. 3.4E38||7-8||4|
|Double||5.0E-324 .. 1.7E308||15-16||8|
|Extended||1.9E-4932 .. 1.1E4932||19-20||10|
|Comp||-2E64+1 .. 2E63-1||19-20||8|
|ByteBool||1||Any nonzero value|
|WordBool||2||Any nonzero value|
|LongBool||4||Any nonzero value|