1. Primitive Data Types
Data Objects
Memory spaces where data values may be stored and later retrieved.
Two types of data objects:
• Programmer-defined data object
Explicitly created and manipulated by the programmer through declarations
and statements in the program.
• System-defined data object
Set up by the virtual computer for housekeeping during program execution
and one that is not accessible to the programmer.
• A data object has attributes. One important attribute is the value type.
• Another attribute is the size.
• Another important consideration in data objects is their lifetime, that is, how long
does the data object exists. This is usually related to when the data object is
created ordestroyed.
Data Values and Values Types
Value
Anything that may be evaluated, stored, passed as argument to a procedure,
returned by a function; or given as a component of a data structure.
Value Type
A set of values. In programming language, the types of values are either of
primitive type or composite type. Other languages have recursive types.
Types of Values:
• Primitive Type
One whose value is atomic and therefore cannot be decomposed.
• Composite Type
A type whose values are composed or structured from simpler values.
• Recursive Type
A special case of composite type where the values are of the same type.

2. Data Types
Data Type
A classification of data, which can store a specific type of information. Data types
are primarily used in computer programming, in which variables are created to
store data.
Primitive Data Type
Predefined types of data, which are supported by the programming language. For
example, integer, character, and string are all primitive data types. Programmers
can use these data types when creating variables in their programs.
Numeric Data Type
All programming languages have some form of numeric data types. The most
common are the integer and real number types.
An example is C, where the type int (integer) has an added attribute for the
number of bytes used to represent the integer. This results in two types of integer
types: long and short.
Example: short i;
long k;
Subrange Type
Introduced to save on storage and for better type checking.
Enumeration Type
A special data type that enables for a variable to be a set of predefined constants.
The variable must be equal to one of the values that have been predefined for it.
Common examples include compass directions (values of NORTH, SOUTH, EAST,
and WEST) and the days of the week.
Boolean or Truth Value Type
A data type having one of the two possible values, true or false.
Character Type
Found in almost programming language. The natural extension is the character-
string data type.
Example:char letter;
letter = 'A';

3. Declarations
A declaration statement is used to declare a variable by specifying its data type
and name.
Example:int number = 10;
booleanisFinished = false;
String welcomeMessage = "Hello!";
Two types of declarations:
1. Explicit-done by the programmer.
2. Implicit - found in languages where data objects are created whenever they are
about to be used.
An explicit declaration serves several purposes both for the programmer and the
language translator. Some of these purposes are:
1. Choice of storage representation
With this information, the translator can make arrangement to allocate the right
amount of storage for a variable.
2. Storage management
This information is very useful for managing the storage during run time.
3. Generic operations
With declaration of variables, overloaded operations can easily be supported and
efficiently implemented.
4. Type Checking
The main purpose of a declaration in most languages is to facilitate static type
checking.
Binding
Describes how a variable is created and used (or "bound") by and within the given
program and, possibly, by other programs, as well.
Classes of Binding:
1. Binding performed at execution time
2. Binding performed at translation time
3. Binding performed at language definition time as another class
4. Binding that occurs at implementation time
Type Checking
Done to ensure that an operation is provided with the correct types.Consider for

4. example the operation, a := b + c;
Two types of Type Checking:
1. Static – done during compilation
2. Dynamic – done during execution
Type Equivalence
When two data objects are involved in one operation, the issue of type
equivalence arises.
Type Conversion and Coercion
Type Conversion
An operation that converts a data object of one type and produces the
corresponding data object in another type.
Example:
Coercion
Process by which a compiler automatically converts a value of one type into a
value of another type when that second type is required by the surrounding
context.
Example:
Initialization
When an elementary data type is declared, a memory location is created for it. To
give the data type an initial value, an assignment statement may be explicitly
written at the beginning of the program.
Example: inti = 1;