Study Note:CSIN3 Chapter 2: C# Language Basic

 

I should familiar with this chapter. If not, I should hit the wall.

 

2.1 A First C# Program

I'm very glad to see the first C# program is not a hello world program. :-)

The first program introduce the variable, method, Main, Class, Namespace.

Nothing important to me, I think.

 

2.2 Syntax

Identifiers: The name of the class, method, variable, namespace and so on. Start with Unicode character or under score. C# is case-sensitive.

Keywords: The words system choose which can't be an identifier, reserved word. You can use prefix @ to use a keyword as identifier. Then you can use it like "@class". But if you use prefix @ to a common identifier, the "@a" and "a" is the same.

Contextual Keywords: I don't know it exactly, maybe they are recognized as keywords in special area.

Literals: Data in the code.

Punctuators: Separator. E.g. , ; {}

Operators: Transform and combine expressions. E.g. + - * /

Comments: // single line comment /* */ multiline comment

 

I decide to not note all the things, it is too much to note, oops. I just note the useful information.

 

2.3 Type Basics

1. Predefine types and Custom types
2. Value types, Reference types and Pointer types
   • Different of value type and reference type
     • Memory allocate: value just an object, reference has a reference and an object
     • Copy: value copy the object, reference copy the reference means point the same object
    
3. Struct is a Custom Value type

 

2.4 Numeric Types

Numeric Literal inference: I use to think is totally wrong.

If there is a decimal point then the literal is a double , else it is a int or long and so on

Checked and Unchecked operator

Real number rounding error: see some statements

decimal m = 1M / 6M;               // 0.1666666666666666666666666667M
double d = 1.0 / 6.0;             // 0.16666666666666666
decimal notQuiteWholeM = m+m+m+m+m+m; // 1.0000000000000000000000000002M
double notQuiteWholeD = d+d+d+d+d+d; // 0.99999999999999989

So don't use float or double to financial calculation, I think.

 

2.5 Boolean Type and Operators

Bool alias System.Boolean

Bool value can't convert to numeric types

Condition operators(&& || !) short-circuit evaluation when possible, &, | don't do short-circuit evaluation

 

2.6 Strings and Characters

Escape characters: /u Unicode

@: verbatim string

 

2.7 Arrays

Declaration:

C#: int[] array = new int[5]; In actually, int[] array is declaration, and new int[5] is initialize

C++: int array[5];

Default initialize: value type 0 or false and so on, reference type is null

Multidimensional array:

rectangular array: int[,] array = new int[3,3];

Jagged Array: int[][] array = new int[3][]; array[0] = new int[4];

Var: I think it will be introduce more in later chapter

 

2.8 Variables and Parameters

Memory allocate: stock and heap

Stock: local variables and parameters

Heap: New objects

Definite Assignment:

• Local variables must be assigned a value before they can be read.
• Function arguments must be supplied when a method is called.
• All other variables (such as fields and array elements) are automatically initialized by the runtime.

Default Value:

Reference null

Numeric type or Enum type 0

char type '/0'

bool type false

Parameter pass style

None

 Value

Going in

Ref

 Reference

Going in

Out

 Reference

Going out

 

 

2.9 Expression and Operators

Operator Precedence

 

2.10 Statements

Goto in switch

Goto case 12;

 

2.11 Namespace

Some advantage feature: I don't think it is very import, and I don't know some of them well, NEED TO READ AGAIN