Primitive Types and Expressions

Class

•  Data or Attributes
  • state of the application
•  Methods or Functions
  • have behavior

Namespace

• is a container for related classes

 Assembly (DLL or EXE)

• is a container for related namespaces
• is a file which can either be a EXE or  a DLL

 Application

• include one or more assemblies

Primitive Types (C# type)

• Integral Number
  • byte (1byte, Max is 255)
  • short
  • int
  • long

• Real Numbers
  • float (4byte)
  • double
  • decimal

• Character
  • char (2byte)

• Boolean
  • bool (1byte)
  • good practice
    • Prefix Boolean names with is or has
    • For example: isOver18, isCitizen, isEligible

Something tricky about real  numbers

• data type is double by default

• wrong

float number = 1.2;

decimal number = 1.2;

• right

float number = 1.2f;

decimal number = 1.2m;

Non-Primitive Types

• String
• Array
• Enum
• Class

Overflowing

• for example

byte number = 255;

number = number + 1;  //0

• if you use check keyword, overflow will not happen and instead the program will throw an exception (But don‘t use it in real world )

Scope

• where a variable / constant has meaning

Type Conversion

• implicit type conversion

byte a = 1;
int b = a;

• explicit type conversion (casting)

int c = 1;
byte d = (byte)c;

• conversion between non-compatible types

string e = "100";
int f = int.Parse(e)

var a = "1234";
int b = Convert.ToInt32(a);

C# Operators

• Arithmetic Operators
  • +
  • -
  • *
  • /

var a = 10;
var b = 3;
Console.WriteLine(a+b); // 3
Console.WriteLine((float)a / (float)b); // 3.333333

• • %
  • Postfix increment

int a = 1;
int b = a++; //b = 1, a = 2;

• • Prefix increment

int a = 1;

int b = ++a; //b = 2, a = 2;

• Comparison Operators
  • ==
  • !=
  • > 
  • >=
  • < 
  • <=

• Assignment
  • =
  • +=
  • -=
  • *=
  • /=

• Logical Operator
  • &&
    
    • And
    • double ampersand
    • a&&b
  • ||
    • Or
    • double vertical line
    • a||b
  • !
    • Not
    • exclamation mark
    • !a

• Bitwise Operators
  • &  And
  • |  Or

Comments

• Single-line Comment

// Here is a single-line comment

• Multi-line Comments

/*

Here is a multi-line

comment

*/

• When to use comments
  
  • to explain whys, hows, constrains, etc
  • Not explain the whats.
    • comment do not explain what the code is doing

Primitive Types and Expressions

原文：http://www.cnblogs.com/jarodli/p/8016168.html