DELEGATES IN C#

DELEGATES IN C#

A delegate type represents references to methods with a particular parameter list and return type.
Delegates make it possible to treat methods as entities that can be assigned to variables and passed as parameters.
Delegates are similar to the concept of function pointers found in some other languages, but unlike function pointers, delegates are object-oriented and type-safe.
The following example declares and uses a delegate type named Function.

using System;
delegate double Function(double x);

class Multiplier
{
double factor;
public Multiplier(double factor) {
this.factor = factor;
}
public double Multiply(double x) {
return x * factor;
}
}
class Test
{
static double Square(double x) {
return x * x;
}
static double[] Apply(double[] a, Function f) {
double[] result = new double[a.Length];
for (int i = 0; i < a.Length; i++) result[i] = f(a[i]);
return result;
}
static void Main() {
double[] a = {0.0, 0.5, 1.0};
double[] squares = Apply(a, Square);
double[] sines = Apply(a, Math.Sin);
Multiplier m = new Multiplier(2.0);
double[] doubles = Apply(a, m.Multiply);
}
}
An instance of the Function delegate type can reference any method that takes a double argument and returns
a double value. The Apply method applies a given Function to the elements of a double[], returning a double[]
with the results. In the Main method, Apply is used to apply three different functions to a double[].

A delegate can reference either a static method (such as Square or Math.Sin in the previous example) or an instance method (such as m.Multiply in the previous example). A delegate that references an instance method also references a particular object, and when the instance method is invoked through the delegate, that object becomes this in the invocation.Delegates can also be created using anonymous functions,which are “inline methods” that are created on the fly. Anonymous functions can see the local variables
of the sourrounding methods. Thus, the multiplier example above can be written more easily without using a Multiplier class:
double[] doubles = Apply(a, (double x) => x * 2.0);
An interesting and useful property of a delegate is that it does not know or care about the class
of the method it references; all that matters is that the referenced method has the same parameters and
return type as the delegate.

INDEXERS in C#

INDEXERS in C#

An indexer is a member that enables objects to be indexed in the same way as an array. An indexer is declared like a property except that the name of the member is this followed by a parameter list written between the delimiters [ and ]. The parameters are available in the accessor(s) of the indexer. Similar to properties, indexers can be read-write, read-only, and write-only, and the accessor(s) of an indexer can be virtual.
The List class declares a single read-write indexer that takes an int parameter. The indexer makes it possible to index List instances with int values. For example
List names = new List();
names.Add("Liz");
names.Add("Martha");
names.Add("Beth");
for (int i = 0; i < names.Count; i++) {
string s = names[i];
names[i] = s.ToUpper();
}
Indexers can be overloaded, meaning that a class can declare multiple indexers as long as the number or types of their parameters differ.

OUTPUT PARAMETER IN C#

OUTPUT PARAMETER IN C#

An output parameter is used for output parameter passing. An output parameter is similar to a reference parameter except that the initial value of the caller-provided argument is unimportant. An output parameter is declared with the out modifier. The following example shows the use of out parameters.
using System;
class Test
{
static void Divide(int x, int y, out int result, out int remainder) {
result = x / y;
remainder = x % y;
}
static void Main() {
int res, rem;
Divide(10, 3, out res, out rem);
Console.WriteLine("{0} {1}", res, rem); // Outputs "3 1"
}

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C# code samples in MSDN Free Download

C# code samples in MSDN Free Download

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Introduction to Merge Statement – One Statement for INSERT, UPDATE, DELETE

Introduction to Merge Statement – One Statement for INSERT, UPDATE, DELETE

MERGE is a new feature that provides an efficient way to perform multiple DML operations.
One of the most important advantage of MERGE statement is all the data is read and processed only once. In previous versions three different statement has to be written to process three different activity (INSERT, UPDATE or DELETE), however using MERGE statement all update activity can be done in one pass of database table. This is quite an improvement in performance of database query.

Consider there are two tables StudentDetails and StudentTotalMarks


In our example we will consider three main conditions while we merge this two tables.
1. Delete the records whose marks are more than 250.
2. Update marks and add 25 to each as internals if records exist.
3. Insert the records if record does not exists
MERGE StudentTotalMarks AS stm
USING (SELECT StudentID,StudentName FROM StudentDetails) AS sd
ON stm.StudentID = sd.StudentID
WHEN MATCHED AND stm.StudentMarks > 250 THEN DELETE
WHEN MATCHED THEN UPDATE SET stm.StudentMarks = stm.StudentMarks + 25
WHEN NOT MATCHED THEN
INSERT(StudentID,StudentMarks)
VALUES(sd.StudentID,25);
GO



There are two very important points to remember while using MERGE statement.
• Semicolon is mandatory after the merge statement.
• When there is a MATCH clause used along with some condition, it has to be specified first amongst all other WHEN MATCH clause.

Insert Multiple Rows in a single statement in Sql Server 2008

Insert Multiple Rows in a single statement in Sql Server 2008

In SQL Server 2008, This new feature enables the developer to insert multiple rows in a single SQL Statement.


insert into insertbulk (name,age) values ('arun',19),('prakash',23),('rajesh',22)