DATA TYPES in C#.[dot]NET

DATA TYPES

Memory Locations for Data

•         Identifier

–        Name

–        Rules for creating an identifier

•         Combination of alphabetic characters (a-z and A-Z), numeric digits (0-9), and the underscore 

•         First character in the name may not be numeric

•         No embedded spaces – concatenate (append) words together

•         Keywords cannot be used

•         Use the case of the character to your advantage

•         Be descriptive with meaningful names

Reserved Words in C#

Naming Convention

•         For Class, method, namespace, and property identifiers

–        First letter of each word capitalized

•         For Variables and Objects

–        First letter of identifier lowercase; first letter of subsequent concatenated words capitalized

–        First letter of variable name indicates its data type (I –int, f –float, d – double, b – boolean (not used in text)

–         For Constant Literals

–        All letters of identifier in upper case

–        Underscore between words of identifier name

Variables

•         Area in computer memory where a value of a particular data type can be stored

–        Declare a variable

–        Allocate memory

•         Syntax – Simple Declaration

–        type identifier; e.g.:   

–        double dTotSales;

•         Syntax – Declaration &Compile-time initialization

–        type identifier = expression; e.g.

–        double dTaxRate = .125;  

Types, Classes, and Objects

•         Type

–        C# has more than one type of number

–        int type is a whole number

–        floating-point types can have a fractional portion

•         Types are actually implemented through classes

–        One-to-one correspondence between a class and a type

–        Simple data type such as int, implemented as a class 

•         Instance of a class → object

•         A class includes more than just data

•         Encapsulation → packaging of data and behaviors into a single or unit→class

Type, Class, and Object Examples 

Predefined Data Types

•         Common Type System (CTS)

•         Divided into two major categories

Figure 3-1 .NET common types

Value and Reference Types

Figure 3-2 Memory representation for value and reference types

Value Types

•         Fundamental or primitive data types

Figure 3-3 Value type hierarchy

Integral Data Types

•         Primary difference

–        How much storage is needed

–        Whether a negative value can be stored

Floating-point Types

•         May be in scientific notation with an exponent

•         n.ne±P

–        3.2e+5 is equivalent to 320,000          

–        1.76e-3 is equivalent to .00176 

•         OR in standard decimal notation

•         Default type is double  

Examples of Floating-point Declarations

double extraPerson = 3.50;     // extraPerson originally set

                                                // to 3.50

double averageScore = 70.0;  // averageScore originally set

                                                // to 70.0

double priceOfTicket;            // cost of a movie ticket

double gradePointAverage;    // grade point average

float totalAmount = 23.57f;   // note the f must be placed after               

                                               // the value for float types

Decimal Types

•         Monetary data items

•         As with the float, must attach the suffix ‘m’ or ‘M’ onto the end of a number to indicate decimal

–        Float attach ‘f’ or “F’

•         Examples

decimal endowmentAmount = 33897698.26M;

decimal deficit;

Boolean Variables

•         Based on true/false, on/off logic

•         Boolean type in C# → bool

•         Does not accept integer values such as 0, 1, or -1

bool undergraduateStudent;

bool moreData = true;