Week 6: THE C# LANGUAGE

C#4.0Week 6:

THE C# LANGUAGE

Flow Control

C#4.0

Slide 2

Data Types

Boolean Byte (0 to 255) Char Date String Decimal Object

Short (-32,768 to 32,767) Integer (-2,147,483,648 to

2,147,483,647) Long (larger whole numbers) Single (floating point accuracy

to 6 digits) Double (floating point accuracy

to 14 points)

C#4.0

Slide 3

Data Types – Memory Usage

Boolean – 1 bytes Byte – 1 byte Char – 2 bytes Date – 8 bytes String – varies Decimal – 16 bytes Object –

Short – 2 bytes Integer – 4 bytes Long – 8 bytes Single – 4 bytes Double – 8 bytes

C#4.0

Slide 4

Data Types – Prefixes

Boolean – bln Byte – byt Char – chr Date – dat String – str Decimal – dec Object – depends

on type of object

Short – sht Integer – int Long – lng Single – sng Double – dbl

C#4.0

Slide 5

Declaration Statements Declare Variables

int intNumberOfStudents ; CONST used to declare Named Constants

Const single sngDISCOUNT_RATE = 0.2f; Declaration includes

Name, follow Naming Convention Rules Data Type Required Value for Constants Optional Initial Value for Variables

C#4.0

Slide 6

Type-Declaration Characters Append single character to the end of the

Constant's Value to indicate the Data Type• Decimal – m • Single – F• Double

Const Single sngDISCOUNT_RATE = 0.2F;

C#4.0

Slide 7

Declaration Examples

string strName, strSSN ;int intAge; decimal decPayRate ;decimal decTax=0.1M ;bool blnInsured ;long lngPopulation ;decimal decDT, decCD, decCR;decimal decHour, decSumSal, decDiemTB, decSum=0;decimal decTax = 0.12M, decHSLuong=3.16M;const decimal decDISCOUNT_RATE = 0.15M;

C#4.0

Slide 8

Scope Declaring & Naming (*)

Public g prefix Declare in General Declarations as Public

Module/Private m prefix Declare in Module’s General Declarations as Private

Local no prefix required Declare in Event Procedures

String gstrName ;

String mstrName;

String strName ;

C#4.0

Slide 9

Scope Public

Available to all modules and procedures of Project Module/Private (Form)

Can be used in any procedure on a specific Form, but is not visible to other Forms

Initialized 1st time the Form is loaded Local

Available only to the procedure it is declared in Initialized every time the Procedure runs

Block (not used until later in this course) Available only to the block of code inside a procedure it is

declared in Initialized every time the Procedure runs

C#4.0

Slide 10

Declaring Local Level Variables Example

Local Level Variables

C#4.0

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Declaring Module Level Variables Example

Module - Level Variables and Constants

C#4.0

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Declaring Block Level Variables Example

int a,b;

if (a > b)

{

int max;

max = a;

}

else

{

int max1;

max1=max Được không??

max1 = b;

}

Block Level Variables

Block Level Variables

C#4.0

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Math Class Methods (p 192) The Math class

Allows the user to perform common math calculations

Using methodsClassName.MethodName( argument1,

arument2, … ) Constants

Math.PI = 3.1415926535…Math.E = 2.7182818285…

C#4.0

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9:06:37 AM

Math Class MethodsMethod Example Abs( x ) Abs( 23.7 ) is 23.7 Ceiling( x ) Ceiling( 9.2 ) is 10.0

Ceiling( -9.8 ) is -9.0 Cos( x ) Cos( 0.0 ) is 1.0

Exp( x ) Exp( 1.0 ) is approximately 2.7182818284590451

Floor( x ) Floor( 9.2 ) is 9.0 Floor( -9.8 ) is -10.0

Log( x ) Log( 2.7182818284590451 ) is approximately 1.0

Max( x, y ) Max( 2.3, 12.7 ) is 12.7 Max( -2.3, -12.7 ) is -2.3

Min( x, y ) Min( 2.3, 12.7 ) is 2.3 Min( -2.3, -12.7 ) is -12.7

C#4.0

Slide 15

Math Class Methods

Method ExamplePow(x,y) Pow( 2.0, 7.0 ) is 128.0

Pow( 9.0, .5 ) is 3.0

Sin ( x ) Sin( 0.0 ) is 0.0

Sqrt ( x ) Sqrt( 900.0 ) is 30.0Sqrt( 9.0 ) is 3.0

Tan ( x ) Tan( 0.0 ) is 0.0

C#4.0

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Compound Assignment Operators Assignment operators

Can reduce code x += 2 is the same as x = x + 2

Can be done with all the math operators ++, -=, *=, /=, and %=

C#4.0

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Assignment OperatorsAssignment operator Sample expression Explanation Assigns Assume: int c = 3, d = 5, e = 4, f = 6, g = 12;

+= c += 7 c = c + 7 10 to c

-= d -= 4 d = d - 4 1 to d

*= e *= 5 e = e * 5 20 to e

/= f /= 3 f = f / 3 2 to f

%= g %= 9 g = g % 9 3 to g Arithmetic assignment operators.

C#4.0

Slide 18

Increment and Decrement Operators Increment operator

Used to add one to the variable x++ Same as x = x + 1

Decrement operator Used to subtract 1 from the variable y--

C#4.0

Increment and Decrement Operators Pre-increment vs. post-increment

x++ or x-- Will perform an action and then add to or subtract one

from the value ++x or --x

Will add to or subtract one from the value and then perform an action

Windows Programming 1 Slide 19

C#4.0

Slide 20

Increment and Decrement Operators

Operator Called Sample expression Explanation ++ preincrement ++a Increment a by 1, then use the new value

of a in the expression in which a resides.

++ postincrement a++ Use the current value of a in the expression in which a resides, then increment a by 1.

-- predecrement --b Decrement b by 1, then use the new value of b in the expression in which b resides.

-- postdecrement b-- Use the current value of b in the expression in which b resides, then decrement b by 1.

Fig. 5.13 The increment and decrement operators.

C#4.0

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Increment and Decrement Operators

Operators Associativity Type () ++ --

left to right right to left

parentheses unary postfix

++ -- + - (type) right to left unary prefix

* / % left to right multiplicative

+ - left to right additive

< <= > >= left to right relational

== != left to right equality

?: right to left conditional

= += -= *= /= %= right to left assignment

Precedence and associativity of the operators discussed so far in this book.

C#4.0

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Format CodeFormat Code Description

C or c Formats the string as currency. Precedes the number with an appropriate currency symbol ($ in the US).

D or d Formats the string as a decimal. Displays number as an integer.

N or n Formats the string with commas and two decimal places.

E or e Formats the number using scientific notation with a default of six decimal places.( 14000 = 1, 4 x 10 Ư 4)

F or f Formats the string with a fixed number of decimal places (two by default).

G or g General. Either E or F.

X or x Formats the string as hexadecimal.

C#4.0

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Example

lblCommission.Text =

string.Format("{0:C}",decCommission);

C#4.0

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Format Code

C#4.0

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Logical and Conditional Operators Operators

Logical AND (&) Conditional AND (&&) Logical OR (|) Conditional OR (||) Logical exclusive OR or XOR (^) Logical NOT (!)

Can be avoided if desired by using other conditional operators

Used to add multiple conditions to a statement

C#4.0

Slide 26

Logical and Conditional Operatorsexpression1 expression2 expression1 &&

expression2 false false false false true false true false false true true true Truth table for the && (logical AND) operator. expression1 expression2 expression1 ||

expression2 false false false false true true true false true true true true Truth table for the || (logical OR) operator.

C#4.0

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Logical and Conditional Operatorsexpression1 expression2 expression1 ^

expression2 false false false false true true true false true true true false Truth table for the logical exclusive OR (^) operator. expression !expression false true True false Truth table for operator! (logical NOT).

C#4.0

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Structured Programming Summary

Operators Associativity Type () ++ --

left to right right to left

parentheses unary postfix

++ -- + - ! (type) right to left unary prefix

* / % left to right multiplicative

+ - left to right additive

< <= > >= left to right relational

== != left to right equality

& left to right logical AND

^ left to right logical exclusive OR

| left to right logical inclusive OR

&& left to right conditional AND

|| left to right conditional OR

?: right to left conditional

= += -= *= /= %= right to left assignment

Precedence and associativity of the operators discussed so far.

C#4.0

Slide 29

Mathematical Examples

Thứ tự thưc hiện

C#4.0

Slide 30

Control Structures Program of control

Program performs one statement then goes to next line Sequential execution

Different statement other than the next one executes Selection structure

The if and if/else statements The goto statement

No longer used unless absolutely needed Causes many readability problems

Repetition structure The while and do/while loops (chapter 5) The for and foreach loops (chapter 5)

C#4.0

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Control Structures

add grade to total

add 1 to counter

total = total + grade;

counter = counter + 1;

Fig. 5.1 Flowcharting C#’s sequence structure.

C#4.0

Slide 32

if Selection Structure The if structure

Causes the program to make a selection Chooses based on conditional

Any expression that evaluates to a bool type True: perform an action False: skip the action

Single entry/exit point Require no semicolon in syntax

C#4.0

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if Selection Structure

Fig. 5.3 Flowcharting a single-selection if structure.

do somethingconditionstrue

false

C#4.0

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if/else selection structure The if/else structure

Alternate courses can be taken when the statement is false

Rather than one action there are two choices Nested structures can test many cases Structures with many lines of code need braces

({) Can cause errors

Fatal logic error Nonfatal logic error

C#4.0

Slide 35

if/else Selection Structure

Fig. 5.4 Flowcharting a double-selection if/else structure.

Conditions

do somethingdo something else

false true

C#4.0

Slide 36

Conditional Operator (?:) Conditional Operator (?:)

C#’s only ternary operator Similar to an if/else structure The syntax is:

boolean value ? if true : if false

Console.WriteLine( grade >= 60 ? "Passed" : "Failed" );

C#4.0

Slide 37

Loops Repeating a series of instructions Each repetition is called an iteration Types of Loops

Do Use when the number of iterations is unknown

For Use when the number of iterations known

C#4.0

Slide 38

while Repetition Structure

Fig. 4.5 Flowcharting the while repetition structure.

true

false

do somethingconditions

C#4.0

Slide 39

for Repetition Structure The for repetition structure

Syntax:for (Expression1, Expression2, Expression3) Expression1 = names the control variable

Can contain several variables Expression2 = loop-continuation condition Expression3 = incrementing/decrementing

If Expression1 has several variables, Expression3 must have several variables accordingly

++counter and counter++ are equivalent

C#4.0

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9:06:37 AM

for Repetition Structure

for ( int counter = 1; counter <= 5; counter++ )

Initial value of control variable Increment of control variable

Control variable name Final value of control variablefor keyword

Loop-continuation condition

Fig. 5.3 Components of a typical for header.

C#4.0

Slide 41

for Repetition Structure

counter++

Establish initial value of control variable.

Determine if final value of control variable has been reached.

counter <= 10 Console.WriteLine( counter * 10 );

true

false

int counter = 1

Body of loop (this may be multiple statements)

Increment the control variable.

Fig. 5.4 Flowcharting a typical for repetition structure.

C#4.0

Slide 42

switch Multiple-Selection Structure

switch (<Biểu Thức>){ Case Giá trị 1 :

[ code to run] break;

Case Giá trị 2 : [ code to run]

break;[default ]

[code to run]]}

If expression=value in constant list

If expression< >values in any of the preceding constant lists

C#4.0

Slide 43

Flocharting Switch Multiple Selection Structure.

Case a: Actions a break;

Case b: Actions b break;

Case n: Action n break;

default break;

true

true

true

true

false

false

false

C#4.0

Slide 44

SwitchCase - Numeric Value Example 1switch ( intScore) { case 100:

lblMsg.Text="Excellent Score"; break; case 99:

lblMsg.Text="Very Good"; break; case 79:

lblMsg.Text="Excellent Score"; break; default:

lblMsg.Text="Improvement Needed"; break; }

C#4.0

Slide 45

9:06:37 AM

do/while Repetition Structure The while loops vs. the do/while loops

Using a while loop Condition is tested The the action is performed Loop could be skipped altogether

Using a do/while loop Action is performed Then the loop condition is tested Loop must be run though once Always uses brackets ({) to prevent confusion

C#4.0

Slide 46

do/while Repetition Structure

true

false

action(s)

condition

Fig. 5.13 Flowcharting the do/while repetition structure.

C#4.0

Slide 47

9:06:37 AM

MessageBox Object Use Show Method of MessageBox to display

special type of window Arguments of Show method

Message to display Optional Title Bar Caption Optional Button(s) Optional Icon

C#4.0

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9:06:37 AM

MessageBox Syntax

MessageBox.Show (TextMessage, TitlebarText, _ MessageBoxButtons, MesssageBoxIcon)

The MessageBox is an Overloaded Method Overloading – ability to call different versions of a procedure

based on the number and data types of the arguments passed to that procedure

The number and data types of the arguments expected by a procedure are called Signatures

There are multiple Signatures to choose from Arguments must be included to exactly match one of the

predefined Signatures

C#4.0

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9:06:37 AM

MessageBoxIcon ConstantsMessageBox Icons Icon Description MessageBoxIcon.Exclamation

Displays a dialog with an exclamation point. Typically used to caution the user against potential problems.

MessageBoxIcon.Information

Displays a dialog with an informational message to the user.

MessageBoxIcon.Question

Displays a dialog with a question mark. Typically used to ask the user a question.

MessageBoxIcon.Error

Displays a dialog with an x in a red circle. Helps alert user of errors or important messages.

Fig. 5.6 Icons for message dialogs.

C#4.0

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9:06:37 AM

MessageBoxButtonMessageBox Buttons Description MessageBoxButton.OK Specifies that the dialog should

include an OK button.

MessageBoxButton.OKCancel Specifies that the dialog should include OK and Cancel buttons. Warns the user about some condition and allows the user to either continue or cancel an operation.

MessageBoxButton.YesNo Specifies that the dialog should contain Yes and No buttons. Used to ask the user a question.

MessageBoxButton.YesNoCancel Specifies that the dialog should contain Yes, No and Cancel buttons. Typically used to ask the user a question but still allows the user to cancel the operation.

MessageBoxButton.RetryCancel Specifies that the dialog should contain Retry and Cancel buttons. Typically used to inform a user about a failed operation and allow the user to retry or cancel the operation.

MessageBoxButton.AbortRetryIgnore Specifies that the dialog should contain Abort, Retry and Ignore buttons. Typically used to inform the user that one of a series of operations has failed and allow the user to abort the series of operations, retry the failed operation or ignore the failed operation and continue.

Fig. 5.7 Buttons for message dialogs.

C#4.0

Slide 51

ExDialogResult dl; dl= MessageBox.Show( "Are you sure exit ? ",

"Warning" , MessageBoxButtons.YesNo,

MessageBoxIcon.Question);if (dl == DialogResult.Yes) Close();

C#4.0Week 6:

THE C# LANGUAGE

More Variable

C#4.0

Value types and reference types The .NET type system defines two categories

of data type Value types

Values stored on the stack Derived from System.ValueType Examples of built-in framework value types:

Byte, Int16, Int32, Int64, Single, Double, Decimal, Char, Boolean

C# has built-in types which are aliases for these: byte, short, int, long, float, double, decimal, char, bool

Object Oriented Software Development 53

C#4.0

Value types and reference types Reference types

Objects stored in the heap References stored on the stack Types derived from System.Object Examples of reference types:

String (C# alias is string) all classes, including classes in your project arrays (see later) delegates (see later)


C#4.0

Boxing and unboxing Boxing

Converting value type to reference type

Unboxing Converting reference type to value type

We will look again at boxing and type conversions later

Object Oriented Software Development 4. C# data types, objects and references

55

C#4.0

Creating value types There are two kinds of value type in .NET struct

Similar to a class, but stored as a value type Local variable of struct type will be stored on the

stack Built-in values types, e.g. Int32, are structs

enum An enumeration type Consists of a set of named constants


C#4.0

struct Example in TimeSheet.cs - rewrite

TimeSheet as a struct rather than a class

struct can contain instance variables, constructors, properties, methods

Can’t explicitly declare default constructor Compiler generates default constructor


C#4.0

struct Instance can be created without new key

word

With class, this would create a null reference With struct, this creates instance with fields

set to default values

This explicitly calls default constructor


C#4.0

Method call with struct parameter Revisit earlier example with TimeSheet as a

struct Main creates TimeSheet struct

instance and passes it as a parameter to RecordOvertime Parameter contains a copy of

the struct A copy of whole struct placed

on stack


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Stack

Program.Main

emp1:Employeeloc: Location

emp2:Employee

ts: TimeSheetEmployee.RecordOvertime

hours: intisWeekend: bool

copy

numberOfEntries: intmaxEntries: int

ts: TimeSheetnumberOfEntries: int

maxEntries: int

C#4.0

struct vs. class TimeSheet example is a small struct, but

structs can have large numbers of instance variables

Passing large structs as parameters can use a lot of stack memory

On the other hand, creating objects on the heap is expensive in terms of performance compared to creating structs

No definitive rules, but take these factors into account when deciding


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C#4.0

enum enum is a good way of storing and naming

constant values

Enum has an underlying data type int by default in example, Days.Sat, Days.Sun, Days.Mon...

represent values 0,1, 2,... can set values explicitly


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C#4.0

enum example Previously indicated pay rate with boolean

value isWeekend Replace this with enum, which allows more

than simply true/false


C#4.0

enum example Change parameter in RecordOvertime to type

PayRate


C#4.0

enum example Pass in enumeration value to method

Always refer to value by name, don’t need to know or use underlying value


C#4.0

Warning! Classes, objects, instance variables,

methods, references are fundamental OO concepts

Value types (struct, enum) and properties are specific to the way in which .NET interprets the OO programming model


Week 6: THE C# LANGUAGE

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