Video: C# Data Types (Bulgarian)

Topics covered:

• Primitive Data Types
  • Integer
  • Floating-Point / Decimal Floating-Point
  • Boolean
  • Character
  • String
  • Object
• Declaring and Using Variables
  • Identifiers
  • Declaring Variables and Assigning Values
  • Literals

Video (in Bulgarian)

Presentation Content

How Computing Works?

• Computers are machines that process data
  • Data is stored in the computer memory in variables
  • Variables have name , data type and value
• Example of variable definition and assignment in C#

What Is a Data Type?

• A data type :
  • Is a domain of values of similar characteristics
  • Defines the type of information stored in the computer memory (in a variable)
• Examples:
  • Positive integers: 1 , 2 , 3 , …
  • Alphabetical characters: a , b , c , …
  • Days of week: Monday , Tuesday , …

Data Type Characteristics

• A data type has:
  • Name (C#keyword or .NET type)
  • Size (how much memory is used)
  • Defaultvalue
• Example:
  • Integer numbers in C#
  • Name: int
  • Size:32bits (4bytes)
  • Default value: 0

What are Integer Types?

• Integer types:
  • Represent whole numbers
  • May be signed or unsigned
  • Have range of values, depending on thesize of memory used
• The default value of integer types is:
  • 0 – for integer types, except
  • 0L – for the long type

Integer Types

• Integer types are:
  • sbyte (-128 to 127): signed 8-bit
  • byte (0 to 255): unsigned 8-bit
  • short (-32,768 to 32,767): signed 16-bit
  • ushort (0 to 65,535): unsigned16-bit
  • int (-2,147,483,648 to 2,147,483,647): signed 32-bit
  • uint (0 to 4,294,967,295): unsigned 32-bit

Integer Types (2)

• More integer types:
  • long (-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807): signed 64-bit
  • ulong (0 to 18,446,744,073,709,551,615): unsigned 64-bit

What are Floating-Point Types?

• Floating-point types:
  • Represent real numbers
  • May be signed or unsigned
  • Have range of values and different precision depending on thesizeof memory used
  • Can behave abnormally in the calculations

Floating-Point Types

• Floating-point types are:
  • float (±1.5 × 10−45to±3.4 × 1038):32-bits, precision of7digits
  • double (±5.0 × 10−324to±1.7 × 10308):64-bits, precision of15-16digits
• The default value of floating-point types:
  • Is 0.0F for the float type
  • Is 0.0D for the double type

PI Precision – Example

• See below thedifference in precision when using float and double :
• NOTE: The“ f ”suffix in the first statement!
  • Real numbers are by default interpreted as double !
  • One should explicitly convert them to float

Abnormalities in the Floating-Point Calculations

• Sometimes abnormalitiescan be observedwhen using floating-point numbers
  • Comparing floating-point numbers can not beperformed directlywiththe == operator
• Example:

Decimal Floating-Point Types

• There is a specialdecimal floating-point realnumbertype in C#:
  • decimal (±1,0 × 10-28to±7,9 × 1028): 128-bits, precision of28-29digits
  • Used for financialcalculations
  • No round-offerrors
  • Almost no loss of precision
• The default value of decimal type is:
  • 0.0 M ( M is the suffix for decimal numbers)

The Boolean Data Type

• The Boolean data type :
  • Is declaredbythe bool keyword
  • Has two possible values: true and false
  • Is useful in logical expressions
• The default value is false

The Character Data Type

• The character data type :
  • Represents symbolic information
  • Is declared by the char keyword
  • Gives each symbol a corresponding integer code
  • Has a ‘\0’ default value
  • Takes 16 bits of memory (from U+0000 to U+FFFF )

The String Data Type

• The string data type :
  • Represents a sequence of characters
  • Is declared by the string keyword
  • Has a default value null (no value)
• Strings are enclosed in quotes:
• Strings can beconcatenated
  • Using the + operator

The Object Type

• The object type:
  • Is declared by the object keyword
  • Is thebase typeof all other types
  • Canhold values of any type

What Is a Variable?

• A variable is a:
  • Placeholder of information that can usuallybe changedat run-time
• Variables allow you to:
  • Store information
  • Retrieve the stored information
  • Manipulate the stored information

Variable Characteristics

• A variable has:
  • Name
  • Type (of stored data)
  • Value
• Example:
  • Name: counter
  • Type: int
  • Value: 5

Declaring Variables

• When declaring a variable we:
  • Specify its type
  • Specify its name (called identifier)
  • May give it an initial value
• The syntax is the following:
• Example:

Identifiers

• Identifiers may consist of:
  • Letters (Unicode)
  • Digits [0-9]
  • Underscore “_”
• Identifiers
  • Can begin only with a letter or an underscore
  • Cannot be a C# keyword

Identifiers (2)

• Identifiers
  • Shouldhave adescriptive name
  • It is recommended to use only Latin letters
  • Should be neither too long nor too short
• Note:
  • In C# smallletters are considered different thanthe capitalletters (case sensitivity)

Assigning Values

• Assigning ofvaluestovariables
  • Is achieved by the = operator
• The = operator has
  • Variable identifier on the left
  • Value of the corresponding data type on the right
  • Could be used in a cascade calling, where assigning is done from right to left

Initializing Variables

• Initializing
  • Is assigning of initial value
  • Must be done before the variable is used!
• Several ways of initializing:
  • By using the new keyword
  • By using a literal expression
  • By referring to an already initialized variable

What are Literals?

• Literals are:
  • Representationsofvalues in the source code
• There are six types of literals
  • Boolean
  • Integer
  • Real
  • Character
  • String
  • The null literal

Boolean and Integer Literals

• The boolean literals are:
  • true
  • false
• The integer literals:
  • Are used for variables of type int , uint , long , and ulong
  • Consist of digits
  • May have a sign ( + , - )
  • May be in a hexadecimal format

Integer Literals

• Examples of integer literals
  • The ’ 0x ’ and ’ 0X ’ prefixesmean a hexadecimal value, e.g. 0xA8F1
  • The ’ u ’ and ’ U ’ suffixesmean a ulong or uint type, e.g. 12345678U
  • The ’ l ’ and ’ L ’ suffixesmean a long or ulong type, e.g. 9876543L

Real Literals

• The real literals:
  • Are used for values of type float , double and decimal
  • May consist of digits, a sign and“ . ”
  • May be in exponentialnotation: 6.02e+23
• The“ f ”and“ F ”suffixes mean float
• The “ d ” and “ D ” suffixes mean double
• The “ m ” and “ M ” suffixes mean decimal
• Thedefault interpretation is double

Character Literals

• The character literals:
  • Are used for values of the char type
  • Consist of two single quotes surrounding thecharacter value: ’ <value> ’
• The value may be:
  • Symbol
  • The code of the symbol
  • Escapingsequence

Escaping Sequences

• Escapingsequences are:
  • Means of presenting a symbol that is usually interpreted otherwise (like ’ )
  • Means of presenting system symbols (like the new line symbol)
• Commonescapingsequences are:
  • \’ for singlequote \" for double quote
  • \\ forbackslash \n for newline
  • \uXXXX for denoting any other Unicode symbol

String Literals

• String literals:
  • Are used for values of the string type
  • Consist of two double quotes surrounding the value: " <value> "
  • May have a @ prefix whichignores theusedescaping sequences: @ “<value>”
• The value is a sequence of character literals

Nullable Types

• Nullable types are instances of the System.Nullable struct
  • Wrapper over the primitive types
  • E.g. int? , double? , etc.
• Nullabe type can represent the normal range of values for its underlying value type, plus an additional null value
• Useful when dealing with Databases or other structures that have default value null

Dynamic Types

• Dynamic types in C# (keyword dynamic )
  • Can hold anything (string, number, object, function / method reference)
  • Operations evaluated at runtime
  • Behave like types in JavaScript / PHP