Part 11 to 20 Basic in C# continue

Part 11-12 switch statement in C#

switch statement

break statement   if break statement is used inside a switch statement,he control will leave the switch statement

goto statement    you can either jump to another case statement,or to specific label(label is some word you coding to mark).

　　　　　　　　　Warning:Using goto is bad programming style,we can should avoid go to by all means

Multiple if else statements can be replaced with a switch statement

for an excample:

if(number ==10)
    Console.WriteLine("you number is 10");
else if(number ==20)
    Console.WriteLine("you number is 20");
else if(number ==30)
    Console.WriteLine("you number is 30");
else
    Console.WriteLine("you number is not 10 to 30");

above code can be replaced as:

switch(number)
{
　　case :10
　　Console.WriteLine("you number is 10");
　　break;
　　case :20
　　Console.WriteLine("you number is 20");
　　break;
      case :30
　　Console.WriteLine("you number is 30");
　　break;
      defalut:
　　Console.WriteLine("you number is not 10 to 30");
      break;
}

or can be replaced as:

switch(number)
{
　　case:10
      case:20　　
　　case:30
　　Console.WriteLine("you number is{0}",number);
      break;
　　default:
　　Console.WriteLine("you number is not 10 to 30");
      break;
}

Noted that switch(expression) , expression value must be bool , char, string, int ,enum or nullable type.

Part 13 while loop in c#

1,while loop checks the condition first.

2,if the condition is true,statements with in the loop are executed.

3,this process is repeated as long as the condition evaluetes to true.

Note:Don't forget to update the variable participating in the condition,so the loop can end , at some point

Part 14 do while loop in c#

1,a do loop checks its condition at the end of the loop.

2,this means that the do loop is guranteed to execute at least one time.

3,do loops are used to present a menu to the user

Difference -while & do while

1,while loop checks the condition at the beginning, where as do while loop checks the condition at the end of the loop.

2,do loop is guaranteed to execute at least once, where as while loop is not

Part 15 for and foreach loops in c#

The for loop

A for loop is very similar to while loop. in a while loop we do the initialization at one place, condition check at another place, and modifying the variable at another place,where as for loop has all of these at one place.

foreach loop

A foreach loop is used to iterate through the items in a collection.For example,foreach loop can be used with arrays or collectioins such as ArrayList, HashTable and Generics.

Part 16 Methods in c#

Static Vs Instance methods

static method is invoked using the class name, where are an instance method is invoked using an instance of the class.

the difference between instance methods and static methods is that multiple instances of a class can be created(or instantiated) and each instance has its own separate method. however, when a method is static,there are no instances of that method, and you can invoke only that one definition of the static method

Part 17  Method parameters

The 4 types of method parameters

1,value parameters

2,reference parameters(use ref keyword)

3,out parameters(use out keyword)

4,parameter arrays(use params keyword ,should be the last one in the parameters list,and only have one params paremeter.)

method parameters Vs method arguments

Pass by value/reference:

public static void main()
{
    int i =0;
    Change1(i);      // 0  pass by value
    Change2(ref i); // 1   pass by reference
}
public static void Change1(int j)
{
    j =1;
    Console.Write(j);
}
public static void Change2(ref int j)
{
    j=1;
    Console.Write(j);
}

Pass by value: i and j are pointing to different memory locations. Operations one valiable will not affect the value of the other variable.

Pass by reference: i and j are pointing to the same memory location. Operations one valiable will affect the value of the other variable.

Part 18 namespace

namespaces are used to organize your programs

they also provide assistance(帮助) in avoiding(避免) name clashes(冲突)

namespaces don't correspond(对应) to file, directory(目录) or assembly(程序集) names. they could be wirtten in separate(单独) files and/or separate assemblies and still belong to the same namespace.

Namespaces can be nested(嵌套) in 2 ways.

namespace alias directives(指令).  sometimes you may encounter(遇到) a long namespace and wish to have it shorter. this could improve(提高) readability(可读性) and still avoid(避免) name clashes(冲突) with similarly named methods.

if the name of namespace is to long,you can use 'name'='namespace' to improve readability.

eg:

before:　　using system.subsystem.hello

after:　　  using ssh = system.subsystem.hello

Part 19 Introduction to classes

what is a class

a class consists of(由..组成) data and behavior. class data is represented(代表) by it's fields and behavior is represented by it's methods

Purpose of a class constructor

The purpose of a class constructor is to initialize class fields. A class constructor is automatically called when an instance(实例) of a class is created.

Constructors do not have return values and always have the same name as the class.

Constructors are not mandatory(强制性的). if we do not provide a constructor, a default parameter less constructor is automatically provided.

Constructors can be overloaded by the number and type of parameters.

Part 20 Static and instance class members

Static class members

Instance class members

Difference between static and instance members

An example explaining when you should make certain members static

Static and Instance class memebers

When a class memeber includes a static modifier, the member is called as static member.

When no static modifier is present the member is called as non static member or instance member.

Static members are invoked using class name, where as instance members are invoked using instances(object) of the class.

An instance member belongs to specific instance(object) of a class. if I create 3 objects of a class, I will have 3 sets of instance members in the memory, where as there will ever be only one copy of a static member, no matter how many instances of a class are created.

Note: Class member = field, methods, properties, events, indexers,constructor.

Static constructor

Static constructors are used to initialize static fields in a class.

you declare a static constructor by using the keyword static in front of the constructor name.

Static Constructor is called only once, on matter how many instances you create.

Static constructors are called before instance constructors.