Difference Between Var  & dynamic data type

VAR

• Introduced in C# 3.0

• Statically typed – This means the type of variable declared is decided by the compiler at compile time.

• Need to initialize at the time of declaration.
  e.g., var str="string Type";
  Looking at the value assigned to the variable str, the compiler will treat the variable str as string.

• Errors are caught at compile time.
  Since the compiler knows about the type and the methods and properties of the type at the compile time itself.

• Visual Studio shows intellisense since the type of variable assigned is known to compiler.

• e.g., var Object2;
  
  will  throw a compile error since the variable is not initialized. The compiler needs that this variable should be initialized so that it can infer a type from the value.

• e.g. var obj1=1;
  will compile
  var obj1="string Type";
  
  will throw error since the compiler has already decided that the type of obj1 is System.Int32 when the value 1 was assigned to it. Now assigning a string value to it violates the type safety.

Dynamic

• Introduced in C# 4.0
• Dynamically typed - This means the type of variable declared is decided by the compiler at runtime time.
• No need to initialize at the time of declaration.
  e.g., dynamic strValue; 
strValue=”String Type”; //Works fine and compiles
  strValue=100; //Works fine and compiles
• Errors are caught at runtime
  Since the compiler comes to about the type and the methods and properties of the type at the run time
• Intellisense is not available since the type and its related methods and properties can be known at run time only
• e.g., dynamic object2; 
  will compile;
• e.g., dynamic object2; 
  will compile and run
  dynamic object2="String Type";
• will compile and run since the compiler creates the type for obj1 as System.Int32 and then recreates the type as string when the value “I am a string” was assigned to it.
  
  This code will work fine.