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What is the difference between var and dynamic types in C# 4.0?

Posted By :Jean Paul     Posted Date :September 28, 2010    Points :10   Category :.NET Framework 
var gets processed in the compile time itself and shows any error during compile time itself.

dynamic gets processed in the runtime only and in case of errors it is hidden until runtime.

dynamic was introduced as part of the DLR (Dynamic Language Runtime) in .Net.

dynamic d = new MyClass();

Eventhough the method "InexistingMethod" is not there - it will get compiled and thrown exception in runtime.

You can also find related Interview Question to What is the difference between var and dynamic types in C# 4.0?  below: 

Value type & reference types difference? Example from .NET. Integer & struct are value types or reference types in .NET?

Most programming languages provide builtin data types, such as integers and floatingpointnumbers, that are copied when they are passed as arguments (that is, they are passed by value). In the .NET Framework, these are called value types. The runtime

supports two kinds of value types:
· Builtin
value types
The .NET Framework defines builtin
value types, such as System.Int32 and
System.Boolean, which correspond and are identical to primitive data types
used by programming languages.
· Userdefined
value types
Your language will provide ways to define your own value types, which derive from System.ValueType. If you want to define a type representing a value that is small, such as a complex number (using two floatingpoint numbers),
you might choose to define it as a value type because you can pass the value type efficiently by value. If the type you are defining would be more efficiently passed by reference, you should define it as a class instead.

Variables of reference types, referred to as objects, store references to the actual data. This following are the reference types:
· class
· interface
· delegate
This following are the builtin
reference types:
· object (More...)

What is the difference between "dynamic SQL" and "stored procedure" ?

Dynamic sql is the bunch of statements that dynamically constructed at run time and not stored in database.
Where as Stored procedures are stored in data base in complied form. (More...)

What's the difference between NCHAR and NVARCHAR data types and ?

NCHAR and NVARCHAR data types are both Unicode character data types with a maximum length of 4,000 characters. The main difference between these 2 data types is that an NCHAR data type is fixed-length while an NVARCHAR is variable-length. If the number of characters entered in an NCHAR data type column is less than the specified column length, spaces are appended to it to fill up the whole length.

Another difference is in the storage size wherein the storage size for NCHAR is two times n bytes while for NVARCHAR is two times the number of characters entered (in bytes).

You should use NCHAR data type when the data values in a column are expected to be consistently close to the same size. On the other hand, you should use NVARCHAR when the data values in a column are expected to vary considerably in size.

What's the difference between CHAR and VARCHAR data types ?

CHAR and VARCHAR data types are both non-Unicode character data types with a maximum length of 8,000 characters. The main difference between these 2 data types is that a CHAR data type is fixed-length while a VARCHAR is variable-length. If the number of characters entered in a CHAR data type column is less than the declared column length, spaces are appended to it to fill up the whole length.

Another difference is in the storage size wherein the storage size for CHAR is n bytes while for VARCHAR is the actual length in bytes of the data entered (and not n bytes).

You should use CHAR data type when the data values in a column are expected to be consistently close to the same size. On the other hand, you should use VARCHAR when the data values in a column are expected to vary considerably in size.

What's the difference between SMALLDATETIME and DATETIME data types ?

A datetime data type is date and time data from January 1, 1753 through December 31, 9999, to an accuracy of one three-hundredth of a second (equivalent to 3.33 milliseconds or 0.00333 seconds). Values are rounded to increments of .000, .003, or .007 seconds.

On the other hand, a smalldatetime data type is a date and time data from January 1, 1900, through June 6, 2079, with accuracy to the minute. smalldatetime values with 29.998 seconds or lower are rounded down to the nearest minute; values with 29.999 seconds or higher are rounded up to the nearest minute.

Values with the datetime data type are stored internally by Microsoft SQL Server as two 4-byte integers. The first 4 bytes store the number of days before or after the base date, January 1, 1900. The base date is the system reference date. Values for datetime earlier than January 1, 1753, are not permitted. The other 4 bytes store the time of day represented as the number of milliseconds after midnight.

The smalldatetime data type stores dates and times of day with less precision than datetime. SQL Server stores smalldatetime values as two 2-byte integers. The first 2 bytes store the number of days after January 1, 1900. The other 2 bytes store the number of minutes since midnight. Dates range from January 1, 1900, through June 6, 2079, with accuracy to the minute.

smalldatetime is usually used when you don't need to store the time of the day such as in cases of effectivity dates and expiration dates. datetime is used if the time of the day is needed and up to the second accuracy is required.

Difference between Var vs Dynamic?

Var word was introduced with C#3.5(specifically for LINQ) while dynamic is introduced in C#4.0.
Variables declared with var keyword will get compiled and you can have all its related methods by intellisense while variables declared with dynamic keyword will never get compiled. All the exceptions related to dynamic type variables can only be caught at runtime. (More...)

difference between Var and Dynamic keyword in c#

The Var(Implicit typed local variable) keyword is used to define local variables.In case of Var , the underlying data type is determined at compile time itself based on the initial assignment.Once the initial assignment has been made with Var type , then it will become strongly typed.If you try to store any incompatible value with the Var type it will result in compile time error.

But in Dynamic type, the underlying type is determined only at run time.Dynamic data type is not checked at compile time and also it is not strongly typed.We can assign any initial value for dynamic type and then it can be reassigned to any new value during its life time.

dynamic test="Senthil";
Console.Writeline(test.GetType()) // System.String

Console.Writeline(test.GetType()) // System.Int32

test=new List();
Console.Writeline(test.GetType()) //System.Collections.Generic.List'1[System.String]

It doesn't provide IntelliSense support also.It doesn't give better support when we give work with linq also.Because it doesn't support lambda expressions ,extension methods and anonymous methods.

Check this blog for more info about var and dynamic:-

senthilvijayalakshmi.blogspot.in/2013/03/difference-between-var-and-dynamic.html (More...)

Difference between static and dynamic?

Static : we can mention how many things we need.
Dynamic : we cannot mention it generates depends upon the requirements. (More...)

Difference Between Delete and Truncate

.Delete table is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow.

. Truncate table also deletes all the rows in a table, but it won't log the deletion of each row, instead it logs the de-allocation of the data pages of the table, which makes it faster. Of course, truncate table cannot be rolled back.

. Truncate table is functionally identical to delete statement with no "where clause" both remove all rows in the table. But truncate table is faster and uses fewer system and transaction log resources than delete.

. Truncate table removes all rows from a table, but the table structure and its columns, constraints, indexes etc., remains as it is.

. In truncate table the counter used by an identity column for new rows is reset to the seed for the column.

. If you want to retain the identity counter, use delete statement instead.

. If you want to remove table definition and its data, use the drop table statement.

. You cannot use truncate table on a table referenced by a foreign key constraint; instead, use delete statement without a where clause. Because truncate table is not logged, it cannot activate a trigger.

. Truncate table may not be used on tables participating in an indexed view. (More...)

Difference between assembly manifest & metadata?

assembly manifest - An integral part of every assembly that renders the assembly self-describing. The assembly manifest contains the assembly's metadata. The manifest establishes the assembly identity, specifies the files that make up the assembly implementation, specifies the types and resources that make up the assembly, itemizes the compile-time dependencies on other assemblies, and specifies the set of permissions required for the assembly to run properly. This information is used at run time to resolve references, enforce version binding policy, and validate the integrity of loaded assemblies. The self-describing nature of assemblies also helps makes zero-impact install and XCOPY deployment feasible.

metadata - Information that describes every element managed by the common language runtime: an assembly, loadable file, type, method, and so on. This can include information required for debugging and garbage collection, as well as security attributes, marshaling data, extended class and member definitions, version binding, and other information required by the runtime. (More...)

What is the difference between ref & out parameters?

An argument passed to a ref parameter must first be initialized. Compare this to an out parameter, whose argument does not have to be explicitly initialized before being passed to an out parameter. (More...)

What is the difference between a Struct and a Class?

The struct type is suitable for representing lightweight objects such as Point, Rectangle, and Color. Although it is possible to represent a point as a class, a struct is more efficient in some scenarios. For example, if you declare an array of 1000 Point objects, you will allocate additional memory for referencing each object. In this case, the struct is less expensive.

When you create a struct object using the new operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the new operator. If you do not use new, the fields will remain unassigned and the object cannot be used until all of the fields are initialized.

It is an error to declare a default (parameterless) constructor for a struct. A default constructor is always provided to initialize the struct members to their default values.

It is an error to initialize an instance field in a struct.

There is no inheritance for structs as there is for classes. A struct cannot inherit from another struct or class, and it cannot be the base of a class. Structs, however, inherit from the base class Object. A struct can implement interfaces, and it does that exactly as classes do.

A struct is a value type, while a class is a reference type. (More...)

Difference between type constructor and instance constructor? What is static constructor, when it will be fired? And what is its use?

(Class constructor method is also known as type constructor or type initializer)
Instance constructor is executed when a new instance of type is created and the class constructor is executed after the type is loaded and before any one of the type members is accessed. (It will get executed only 1st time, when we call any static methods/fields in the same class.) Class constructors are used for static field initialization. Only one class constructor per type is permitted, and it cannot use the vararg (variable argument) calling convention. (More...)

What is the difference between Finalize and Dispose (Garbage collection)

Class instances often encapsulate control over resources that are not managed by the runtime, such as window handles (HWND), database connections, and so on. Therefore, you should provide both an explicit and an implicit way to free those resources. Provide implicit control by implementing the protected Finalize Method on an object (destructor syntax in C# and the Managed Extensions for C++). The garbage collector calls this method at some point after there are no longer any valid references to the object.
In some cases, you might want to provide programmers using an object with the ability to explicitly release these external resources before the garbage collector frees the object. If an external resource is scarce or expensive, better performance can be achieved if the programmer explicitly releases resources when they are no longer being used. To provide explicit control, implement the Dispose method provided by the IDisposable Interface. The consumer of the object should call this method when it is done using the object. Dispose can be called even if other references to the object are alive.

Note that even when you provide explicit control by way of Dispose, you should provide implicit cleanup using the Finalize method. Finalize provides a backup to prevent resources from permanently leaking if the programmer fails to call Dispose. (More...)

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