C # is the difference between analysis and as the

1. Type Conversion
   
   • Any type may be converted to its base type, with the implicit conversion is completed;
   • Any type into its derived types must be explicit conversion. As :( type name) object name;
   • Use of any type GetType can obtain accurate object;
   • Convert class basic types can be used to achieve the type of conversion;
   • In addition to other types of string has Parse method for converting a string type substantially corresponding to the type;
   • Value and reference type of conversion is called boxing (Boxing) or unpacking (Unboxing);
2. as / is exemplary
   
   • It is conversion rules:
   • Checking compatibility object type, and returns the result true (false);
   • We will not throw an exception;
   • If the object is null, just return false;
     Example:
     
     

     Object = O. 1 "ABC";   
      2 IF (O IS String) // performing a first type compatibility checking   
      . 3 {   
      . 4 S = String (String) O; // perform a second type of compatibility checking, and convert   
      5 MessageBox.Show ( "conversion successful!");   
      . 6}   
      . 7 the else   
      . 8 {   
      . 9 MessageBox.Show ( "conversion failed!");   
     10}  

     
   • as conversion rules:
   • Checking compatibility object type, and returns the transformed result, if incompatible return null; 
   • We will not throw an exception;
   • If the determination result is empty, then the enforcement type conversion throws NullReferenceException exception; Example:
     

     Object = O. 1 "ABC";   
     2 AS String String S = O; // performing a first type compatibility check, and returns the result   
     . 3 IF (! = Null S)    
     . 4 MessageBox.Show ( "conversion successful!");   
     the else 5   
     6 MessageBox.Show ( "conversion failed!");  

     

     as is less than perform a compatibility check, performance may be a little higher.