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Chapter 2. Core C#

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Microsoft

Objectives

“This chapter surveys the C# language syntax. I introduce

you to the two fundamental kinds of types within the

CLR: value types and reference types. This chapter also

describes namespaces and how you can use them to

logically partition types and functionality within your

applications.”

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Roadmap

2.1. C# Is a strongly Typed Language

2.2. Expression

2.3. Statements and Expressions

2.4. Types and Variabless

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Microsoft

2.1. C# Is a strongly Typed Language



Every variable and object instance in the system is of a

well-defined type



This enables the compiler to check that the operations to

perform on variables and object instance are valid



It is always best to find bugs at compile time rather than

run time



Example:

•

Method ComputeAvg(): computes the average of two integers
and returns the result

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double ComputeAvg( int param1, int param2 )
{

return (param1 + param2) / 2.0;
}

object ComputeAvg( object param1, object param2 )
{

return ((int) param1 + (int) param2) / 2.0;
}

ComputeAvg accepts two

integers and returns a double. If 
passing an instance of Apple 
type, the compiler will complain 
and stop

Convert objects into 
integers

objectkeyword: an alias of 
System.Object class

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Microsoft

Roadmap



2.1. C# Is a strongly Typed Language



2.2. Expression



2.3. Statements and Expressions



2.4. Types and Variabless



2.5. NameSpaces



2.6. Control Flows

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2.2. Expressions



Expressions in C# are identical to expressions in C++ and

Java.



Are built using operands, eg. variables or types within an

application, and operators



Operators can be overloaded



Operators can have different meaning in different contexts

• Eg: the + operator can mean string concatenation using with string operands



C# operator precedence:

• When an expression contains multiple operators, the precedence of the
operators controls the order in which the individual operators are evaluated

• Entries at the top of the table have higher precedence

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Microsoft

Category Expression Description
Primary x.m Member access

x(...) Method and delegate invocation

x[...] Array and indexer access

x++ Post-increment

x-- Post-decrement

new T(...) Object and delegate creation

new T(...){...} Object creation with initializer

new {...} Anonymous object initializer

new T[...] Array creation

typeof(T) Obtain System.Type object for T

checked(x) Evaluate expression in checked context

unchecked(x) Evaluate expression in unchecked context

default(T) Obtain default value of type T

delegate {...} Anonymous function (anonymous method)

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Category Expression Description

Unary +x Identity

-x Negation

!x Logical negation

~x Bitwise negation

++x Pre-increment

--x Pre-decrement

(T)x Explicitly convert x to type T

Multiplicative x * y Multiplication

x / y Division

x % y Remainder

Additive x + y Addition, string concatenation, delegate combination

x – y Subtraction, delegate removal

Shift x << y Shift left

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Microsoft

Category Expression Description
Relational and

type testing

x < y Less than
x > y Greater than

x <= y Less than or equal
x >= y Greater than or equal

x is T Return true if x is a T, false otherwise
x as T Return x typed as T, or null if x is not a T
Equality x == y Equal

x != y Not equal

Logical AND x & y Integer bitwise AND, boolean logical AND

Logical XOR x ^ y Integer bitwise XOR, boolean logical XOR
Logical OR x | y Integer bitwise OR, boolean logical OR

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Roadmap



2.1. C# Is a strongly Typed Language



2.2. Expression



2.3. Statements and Expressions



2.4. Types and Variabless



2.5. NameSpaces

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Microsoft

2.3 Statements and Expressions



The actions of a program are expressed using

statements



Several different kinds of statements:

 A block: consists of a list of statements written between the

delimiters { and }

 Declaration statements: are used to declare local variables and

constants

12

{x=69;y=96}

int a;

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Statements and Expressions(2)

 Epression statements are used to evaluate expressions

 Selection statements are used to select one of a number of

possible statements for execution based on the value of some
expression – if, switch

 Iteration statements are used to repeatedly execute an

embedded statement – while, do, for, foreach

while (i ++< Length) {

if(continue == true) {x=69;}
else {x=96;}

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Microsoft

Statements and Expressions(3)

 Jump statements are used to transfer control - break,

continue, goto, throw, return, and yield

 The try...catch statement is used to catch exceptions that
occur during execution of a block, and the try...finally
statement is used to specify finalization code that is always
executed, whether an exception occurred or not

14

1. while (true) {

2. int n = Console.Read();
3. if (n == 69) break;

4. Console.WriteLine(n);

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Statements and Expressions(4)

 The checked and unchecked statements are used to control
the overflow checking context for integral-type arithmetic

operations and conversions

 The lock statement is used to obtain the mutual-exclusion lock
for a given object, execute a statement, and then release the
lock

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Microsoft

Roadmap



2.1. C# Is a strongly Typed Language



2.2. Expression



2.3. Statements and Expressions



2.4. Types and Variabless



2.5. NameSpaces



2.6. Control Flows

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Value Types and Reference Types



Value types:

•

Living places:
 On the stack

 On the heap: only if they are members of reference types or if they
are boxed

•

Are copied by value by default when passed as parameters to
methods or assigned to other variables



Reference types:

•

Living place: on the heap

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Microsoft

Value Types



Contain directly their value and are customarily created

statically



Initialization: using the new

statement



Derive from System.ValueType



Primitives: int, float, char and bool



Others:

enum, struct

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Reference Types



The lifetime of the resulting object is controlled be

garbage collection services provided by CLR



The reference holds the location of an object created on

the managed heap



Derive from System.Object and created with the

new

keyword

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Microsoft



Example:

20

int i = 123;

string s = "Hello world";
123

s "Hello world"

Value
Type

Reference
Type

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Value Types contain Reference Types



Example:

class

ShapeInfo

{

public string infoString;

public ShapeInfo(string info)

{ infoString = info; }

}

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Microsoft

struct Rectangle
{

public ShapeInfo rectInfo;

public int rectTop, rectLeft, rectBottom, rectRight;

public Rectangle(string info, int top, int left, int bottom, int right)
{

rectInfo = new ShapeInfo(info);

rectTop = top; rectBottom = bottom;
rectLeft = left; rectRight = right;

}

public void Display()
{

Console.WriteLine("String = {0}, Top = {1}, Bottom = {2}," +
"Left = {3}, Right = {4}",

rectInfo.infoString, rectTop, rectBottom, rectLeft, rectRight);

}

Value type

The Rectangle structure 
contains a reference

type member

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static void ValueTypeContainingRefType()
{

Console.WriteLine("-> Creating r1");

Rectangle r1 = new Rectangle("First Rect", 10, 10, 50, 50);

Console.WriteLine("-> Assigning r2 to r1");
Rectangle r2 = r1;

Console.WriteLine("-> Changing values of r2");
r2.rectInfo.infoString = "This is new info!";

r2.rectBottom = 4444;

.
r1.Display();

r2.Display();
Create the
first
Rectangle.

Assign a new
Rectangle to

Change some
values of r2.

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Microsoft

Result:

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Default Variable Initialization



The following categories of variables are automatically

initialized to their default values:

 Static variables.

 Instance variables of class instances.

 Array elements.



For a variable of a reference-type, the default value is

null

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Microsoft

Default Variable Initialization(2)



Value-type’s default constructor:

 All value types implicitly declare a public parameterless instance
constructor called the default constructor

 Default constructor returns the default value for the value type:

26

Value Type Default Value

sbyte, byte, short, ushort, int, uint, 
long, and ulong

char '\x0000'

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Default Variable Initialization(3)

Value Type Default Value

float 0.0f

double 0.0d

decimal 0.0m

bool false

enum-type E 0, converted to the type E

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Microsoft

Implicitly Typed Local Variables

“In C#, every variable declared in the code must have an

explicit type associated with it. But sometimes, when

writing code for strongly typed languages, the amount of

typing needed to declare such variables can be

tedious…”

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Implicitly Typed Local Variables(2)



var

is a new keyword in C# 3.0



Declaring a local variabl using the new var keyword asks

the compiler to reserve a local memory slot and attach

an inferred type to that slot



At compilation time, compiler can initialize variables

without asking the type explicitly



How to use:

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Microsoft

using System;

using System.Collections.Generic;
public class EntryPoint

{

static void Main()
{

var myList = new List<int>();
myList.Add( 1 );

myList.Add( 2 );
myList.Add( 3 );

foreach( var i in myList )
{

Console.WriteLine( i );
}

}
}

An implicitly typed

variable declaration must

include an initialzer

var newValue; // emits error CS0818

var a = 2, b = 1;
var x, y = 4;
Not permited

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Implicitly Typed Local Variables(3)



Restriction:

 var cannot use with multiple variable declarators

var x=69, y=9.6; //Error, Implicitly-typed local variables cannot have

multiple declarators

 Declarator implicitly typed local variables must include a

local-variable-initializer

var x; //Error, no initializer to infer type from

 The local-variable-initializer must be an expression

 The initializer expression must have a compile-time type

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Microsoft

Type Conversion



Many times, it’s necessary to convert intstances of one

type to another



Implicit Conversion:



Explicit Conversion:

int defaultValue = 12345678;

long value = defaultValue;

int smallerValue = (int) value;

public class EntryPoint
{

static void Main()
{

int employeeID = 303;

object boxedID = employeeID;
employeeID = 404;

int unboxedID = (int) boxedID;

System.Console.WriteLine( employeeID.ToString()

);

System.Console.WriteLine( unboxedID.ToString() );
}

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Implicit Conversions



One type of data is automatically converted into another

type of data



No data loss



Implicit Numerical Conversion



Implicit Enumeration Conversion

 Permit the decimal, integer, literal to be converted to any enum

1. long x;

2. int y = 25;

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Microsoft

Implicit Conversions(2)



Implicit Reference Conversion

 From any reference type to object.

 From any class type D to any class type B, provided D is inherited from
B.

 From any class type A to interface type I, provided A implements I.

 From any interface type I2 to any other interface type I1, provided I2
inherits I1.

 From any array type to System.Array.

 From any array type A with element type a to an array type B with

element type b provided A & B differ only in element type (but the same
number of elements) and both a and b are reference types and an

implicit reference conversion exists between a & b.

 From any delegate type to System.Delegate type.

 From any array type or delegate type to System.ICloneable.

 From null type to any reference type.

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Implicit Conversions(3)



Boxing Conversions

 Conversion of any value type to object type

1. int x = 10;

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Microsoft

Explicit Conversions



Using the casting operator ()



May be loss data



Explicit Numerical Conversions



Explicit Enumeration Conversions

 From sbyte, byte, short, ushort, int, uint, long, ulong, char, float,
double or decimal to any enum type.

 From any enum type to sbyte, byte, short, ushort, int, uint, long,
ulong, char, float, double or decimal.

 From any enum type to any other enum type

36

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Explicit Conversions(2)



Explicit Reference Conversions

 From object to any reference type.

 From any class type B to any class type D, provided B is the

base class of D

 From any class type A to any interface type I, provided S is not
sealed and do not implement I.

 From any interface type I to any class type A, provided A is not
sealed and implement I.

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Microsoft

as and is Operators



The as

operator

 is used to perform conversions between compatible reference
types

 The as operator is like a cast operation. However, if the

conversion is not possible, as returns null instead of raising an
exception



The is

operator

 Checks if an object is compatible with a given type

 An is expression evaluates to true if the provided expression is
non-null, and the provided object can be cast to the provided
type without causing an exception to be thrown

 The is operator only considers reference conversions, boxing 
conversions, and unboxing conversions

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Generics



Support for generics is one of the most exciting new

additions to the C# language



Using the generic can define a type that depends upon

another type that is not specified at the point of definition



Example:

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Microsoft

1. public class List
2. {

3. private object[] elements;
4. private int count;

6. public void Add(object element) {

7. if (count == elements.Length) Resize(count*2);
8. elements[count++] = element;

9. }

10.

11. public object this[int index] {
12. get { return elements[index]; }
13. set { elements[index] = value; }

14. }

15.

16. public int Count {

17. get { return count; }

18. }

19. }

1. public class List<ItemType>
2. {

3. private ItemType[] elements;
4. private int count;

6. public void Add(ItemType element) {

7. if (count == elements.Length) Resize(count*2);
8. elements[count++] = element;

9. }

10.

11. public ItemType this[int index] {
12. get { return elements[index]; }
13. set { elements[index] = value; }

14. }

15.

16. public int Count {

17. get { return count; }

18. }

19. }

Generics

40

1. List intList = new List();
2.

3. intList.Add(1);
4. intList.Add(2);

5. intList.Add("Three");
6.

7. int i = (int)intList[0];
1. List intList = new List();
2.

3. intList.Add(1); // Argument is boxed
4. intList.Add(2); // Argument is boxed
5. intList.Add("Three"); // Should be an error
6.

7. int i = (int)intList[0]; // Cast required
1. List<int> intList = new List<int>();

3. intList.Add(1); // No boxing
4. intList.Add(2); // No boxing

5. intList.Add("Three"); // Compile-time error
6.

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Generics(2)



Why generics?

 Type checking, no boxing, no downcasts

 Reduced code bloat (typed collections)



How are C# generics implemented?

 Instantiated at run-time, not compile-time

 Checked at declaration, not instantiation

 Work for both reference and value types

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Microsoft

Generics(3)



Can be used with various types

 Class, struct, interface and delegate



Can be used with methods, parameters and return types



Support the concept of constraints

 One base class, multiple interfaces, new()

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Generics(4)



Type parameters can be applied to

 Class, struct, interface, and delegate types

class Dictionary<KeyType, ValueType> {...}
struct Pair<FirstType, SecondType> {...}
interface IComparer<T> {...}

delegate ResType Func<ArgType, ResType>(ArgType
arg);

Dictionary<string, Customer>
customerLookupTable;

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Microsoft

1. class Array

2. {

3. public static T[] Create<T>(int size) {
4. return new T[size];

5. }

7. public static void Sort<T>(T[] array) {
8. ...

9. }

10. }

1. string[] names = Array.Create<string>(3);
2. names[0] = "Jones";

3. names[1] = "Anderson";
4. names[2] = "Williams";
5. Array.Sort(names);

Generics(5)



Type parameters can be applied to

 Class, struct, interface, and delegate types

 Methods

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1. interface IComparable{int CompareTo(object obj);}
2.

3. class Dictionary<K, V>
4. {

5. public void Add(K key, V value) {
6. ...

7. switch (((IComparable)key).CompareTo(x)) {

8. ...
9. }

10. }

1. interface IComparable{int CompareTo(object obj);}

2. class Dictionary<K, V> where K: IComparable

3. {

4. public void Add(K key, V value) {
5. ...

6. switch (key.CompareTo(x)) {

7. ...
8. }

9. }
10. }

1. interface IComparable<T> {int CompareTo(T obj);}
2.

3. class Dictionary<K, V>: IDictionary<K, V> where

4. K: IComparable<K>,

5. V: IKeyProvider<K>,

6. V: IPersistable,

7. V: new()

8. {

9. ...
10. }

Generics(6)



Constraints

 One base class, multiple interfaces, new()

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Microsoft

Roadmap



2.1. C# Is a strongly Typed Language



2.2. Expression



2.3. Statements and Expressions



2.4. Types and Variabless



2.5. NameSpaces



2.6. Control Flows

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2.5 Namespaces



Need for Namespaces



Using namespace directives



Using alias directives

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Microsoft

Need for Namespaces



Namespaces allow you to create a system to organize

your code



A good way to organize your namespaces is via a

hierarchical system



Placing code in different sub-namespaces can keep your

code organized



using keyword used to work with namespaces:

 Create an alias for a namespace (a using alias).

 Permit the use of types in a namespace, such that, you do not
have to qualify the use of a type in that namespace (a using
directive).

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Using namespace directives

1.

using

System;

2.

class

Hello

3.

{

4.

static void

Main()

5.

{

6.

string

hello = “Hello!”;

7.

Console

.WriteLine(hello);

8.

}

Console is a class of
namespace System.

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Microsoft

Using alias directives



using identifier = namespace-or-type-name ;



For example:

50

1. namespace N1.N2

2. {

3. class A {}

4. }

5. namespace N3

6. {

7. using A = N1.N2.A;
8. class B: A {}

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Standard Namespaces in .NET

Fundamentals

System System.IO

System.AddIn System.Linq

System.Collections System.Reflection

System.ComponentModel System.Resources

System.Configuration System.Runtime

System.Diagnostics System.Security

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Microsoft

Standard Namespaces in .NET(2)

 Windows Presentation Foundation

 System.Windows

 Windows Forms

 System.Drawing

 System.Media

 System.Windows.Forms

 ASP.NET

 System.Web

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Standard Namespaces in .NET(3)

 Communications and Workflow

 System.Messaging

 System.Net

 System.Net.Sockets

 System.ServiceModel

 System.Web.Services

 System.Workflow

 DATA, XML and LINQ

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Microsoft

Roadmap



2.1. C# Is a strongly Typed Language



2.2. Expression



2.3. Statements and Expressions



2.4. Types and Variabless



2.5. NameSpaces



2.6. Control Flows

</div>
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2.6 Control Flow



if-else, switch



while, do-while, and for



foreach

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Microsoft

if-else construct



if (condition)

statement(s)_1 //

The original result

[else

statement(s)_2] //

The alternative result

 condition is a relational or logical expression.

 statement(s)_1 is a statement (or a block of statements) that is

executed if the condition is true.

 statement(s)_2 is a statement (or a block of statements) that is

executed if the condition is false

56

1. if (salary > 2000)

2. Console.Write("Salary is greater than 2k");

1. if (salary > 2000)

2. Console.Write("Salary is greater than 2k");

// The original result

3. else

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Nested if-else Statements

if (condition_1)

statement_1;

else if (condition_2)

statement_2;

else if (condition_3)

statement_3;

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Microsoft

switch (expression)
{

case constant-1: statement(s);
jump-statement
case constant-2: statement(s);

jump-statement
case constant-3:
...
[default: statement(s);
jump-statement]

}

switch Construct

expression represents a value that corresponds to the
associated switch choice

statement(s) is a
statement or
block of

statements that is
executed if the
corresponding
condition is
evaluated true
jump-statement is
a branching
statement to
transfer control
outside the specific
case, such as

break or goto
(explained later)
default deals

with all the
other cases

58

1. using System;
2. class Switch

3. {

4. static void main()

5. {

6. int n = 2;

7. switch (n)

8. {

9. case 1: Console.WriteLine("n=1");

10. break;

11. default: Console.WriteLine("n=2");

12. break;

13. }

14. }

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while Loop



while (control_expression)

statement(s);



control_expression is a condition be satisfied during

the loop execution.



statement(s) is a statement (or the block of statements)

to be executed.

1. using

System;

2. class

WhileLoop

3. {

4. static void

Main()

5. {

6. int

counter=0;

7. while

(counter++ <= 10)

8. {

9. Console

.WriteLine(counter);

10. }

11. }

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Microsoft



do

statement(s)

while (control_expression);



control_expression is a condition to be satisfied during

the loop execution.



statement(s) is a statement (or the block of statements)

to be executed.

60

do-while Loop

1. using

System;

2. class

DoWhileLoop

3. {

4. static void

Main()

5. {

6. int

counter=0;

7. do

8. {

9. Console

.WriteLine(counter);

10. }

11. while

(counter++ <= 10);

12. }

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for Loop



for ([initialization];

[control_expression]; counter_update])

statement(s)



initialization is the counter initialization statement.



control_expression is a condition to be satisfied during

the loop execution.



counter_update is the counter increment or decrement

statement.



statement(s) is the statement or block of statements to

1. using

System;

2. class

ForLoop

3. {

4. static void

Main()

5. {

6. for

(

int

counter = 1;counter<=10;

counter=counter +2)

7. {

8. Console

.WriteLine(counter);

9. }

10. }

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Microsoft

The foreach Loop



foreach (type identifier in expression)

statement(s);



type is the data type, such as int or string.



identifier is the variable name.



expression is the name of the array (or collection).



statement(s) is the statement or block of statements to

be executed.

62

1. using

System;

2. class

ForeachLoop

3. {

4. static void

Main()

5. {

6. int

[,] myIntArray = {{1, 3, 5},

7. {2, 4, 6} };

8. foreach

(

int

i

in

myIntArray)

9. Console

.Write("{0} ", i);

10. }

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Branching Statements



break

 terminates the closest enclosing loop or switch statement in
which it appears



goto:

 goto label;

 is not recommended because it corrupts the program structure

 goto case expression; goto default; (in case struct)


continue

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Microsoft

Branching Statements(2)



return

 terminates execution of the method in which it appears and
returns control to the calling method



throw

 is used to signal the occurrence of an anomalous situation
(exception) during the program execution

 Usually is used with try-catch or try-finally statements

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this site is individual site for ueh students of information management faculty this site provides some students resources of it courses such as computer network data structure and algorithm enterprise resource planning

<b>Chapter 2. Core C# </b>

Objectives

<i>“This chapter surveys the C# language syntax. I introduce</i>

<i>you to the two fundamental kinds of types within the</i>

<i>CLR: value types and reference types. This chapter also</i>

<i>describes namespaces and how you can use them to</i>

<i>logically partition types and functionality within your</i>

<i>applications.”</i>

Roadmap

2.1. C# Is a strongly Typed Language

<i>2.2. Expression</i>

<i>2.3. Statements and Expressions</i>

<i>2.4. Types and Variabless</i>

2.1. C# Is a strongly Typed Language

Every variable and object instance in the system is of a

well-defined type

This enables the compiler to check that the operations to

perform on variables and object instance are valid

It is always best to find bugs at compile time rather than

run time

Example:

•

Roadmap

<i>2.1. C# Is a strongly Typed Language</i>

2.2. Expression

<i>2.3. Statements and Expressions</i>

<i>2.4. Types and Variabless</i>

<i>2.5. NameSpaces</i>

<i>2.6. Control Flows</i>

2.2. Expressions

Expressions in C# are identical to expressions in C++ and

Java.

Are built using operands, eg. variables or types within an

application, and operators

Operators can be overloaded

Operators can have different meaning in different contexts



C# operator precedence:

Roadmap

<i>2.1. C# Is a strongly Typed Language</i>

<i>2.2. Expression</i>

2.3. Statements and Expressions

<i>2.4. Types and Variabless</i>

<i>2.5. NameSpaces</i>

2.3 Statements and Expressions

The actions of a program are expressed using

<i><b>statements</b></i>

Several different kinds of statements:

Statements and Expressions(2)

Statements and Expressions(3)

Statements and Expressions(4)

Roadmap

<i>2.1. C# Is a strongly Typed Language</i>

<i>2.2. Expression</i>

<i>2.3. Statements and Expressions</i>

2.4. Types and Variabless

<i>2.5. NameSpaces</i>

<i>2.6. Control Flows</i>

Value Types and Reference Types

Value types:

•

•



Reference types:

•

Value Types

Contain directly their value and are customarily created

statically

Initialization: using the new

statement

Derive from System.ValueType

Primitives: int, float, char and bool

Others:

enum, struct

Reference Types

The lifetime of the resulting object is controlled be

garbage collection services provided by CLR

The reference holds the location of an object created on

the managed heap