Variables and Data Types

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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:

  • integer
  • 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 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;

</delphi>

From the FPC manual

integer types
Type Range Bytes
Byte 0 .. 255 1
Shortint -128 .. 127 1
Smallint -32768 .. 32767 2
Word 0 .. 65535 2
Integer smallint or longint 2 or 4
Cardinal longword 4
Longint -2147483648 .. 2147483647 4
Longword 0..4294967295 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 types
Type Range Significant digits Bytes
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
Currency -922337203685477.5808 922337203685477.5807 8


boolean types
Type Bytes Ord(True)
Boolean 1 1
ByteBool 1 Any nonzero value
WordBool 2 Any nonzero value
LongBool 4 Any nonzero value
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