Dhanushka's Web Blog

With C# 4.0 you can assign a default value to a parameter when you are declaring a method

e.g.
public static void updateMyCV(string name=”Dhanushka”){ do some task }

you can call the method in following ways
updateMyCV(); //this will assign the default value to the parameter name
updateMyCV(“Athukorala”); //passed in value is assigned to the parameter

As you can see when you are calling these method, parameters in the method becomes optional. We can use this feature coupled with named parameters to define methods with an optional set of parameters.

e.g.
public static void
updateMyCV
(int employeeID, string firstName=”Dhanushka”, string lastName=”Athukorala”)
{ do some task }

When you are declaring a method with optional parameters, required parameters need to come first before any optional parameter declaration, here parameters with default values are considered as optional parameters while others are considered as required. There are several ways to call this method legally.

e.g.

updateMyCV(155,”Tekla”,”Dilrukshi”);
updateMyCV(155,”Tekla”);
updateMyCV(155,lastName: “Dilrukshi”);
updateMyCV(155);

But you cannot call the method in following ways although it makes sense to do so

updateMyCV(); //required parameters need to be passed
updateMyCV(155, ,”Dilrukshi”); //cannot leave gaps between arguments
updateMyCV(“Dilrukshi”,155);
//order has to be maintained if you are not using named arguments in the method call

Let’s say that you wrote a method like this

public static int getVolumeOfCylinder(int radius, int height)
{
return 22/7*radius*radius*height;
}

Now we all know until now we have to know the order of the parameters to call this method correctly, right!
Well not any more with C# 4.0 you can consider the parameter names as labels and call them without considering their declaration order in the following way

getVolumeOfCylinder(height: 10, radius: 5);
getVolumeOfCylinder(radius: 5, height: 10);

And as you have imagined already, named arguments can follow a positional argument but a named argument can never be followed by a positional argument

e.g
getVolumeOfCylinder(5, height: 10); //this will compile
getVolumeOfCylinder(height:10, 5); // this wont

In programming languages such as c# and java we use data structures like arrays and lists to store a set of data in the memory so we can iterate through them and do some processing.
when it comes to sql the alternative solution is the T-SQL CURSOR

The basic steps of using a cursor are as follows
1)Declare a cursor and associate it with a SELECT statement, the basic characteristics of the cursor needs to be defined here as well
2)Open and populate the cursor
3)Fetch a row from the cursor
4)Process the fetched row inside the loop after checking the fetch status
5)close and de-allocate the cursor

lets write a simple cursor and demonstrate the above mentioned steps

--Declare the variables needed, to do the necessary processing
DECLARE @NAME VARCHAR(MAX)

---(1)---
DECLARE myCursor CURSOR FOR
SELECT employee_name FROM EMPLOYEES

* alternatively you can declare a local variable of type CURSOR and set its structure as well
DECLARE @myCursor CURSOR
SET @myCursor= CURSOR FOR SELECT employee_name FROM EMPLOYEES
* you can also set the cursor for read only mode to gain more performance or to update mode to update the rows as you iterate through them
DECLARE myCursor CURSOR READ_ONLY
FOR SELECT employee_name FROM EMPLOYEES
OR
DECLARE myCursor CURSOR
FOR SELECT employee_name FROM EMPLOYEES
FOR UPDATE OF designation

---(2)---
OPEN myCursor
--(3)---
FETCH NEXT FROM myCursor INTO @NAME
---(4)---
WHILE @@FETCH_STATUS = 0
BEGIN
PRINT @NAME
FETCH NEXT FROM myCursor INTO @NAME
END
* here FETCH_STATUS is used to determine the boundary status of the iterator, following are values it returns depending on the situation
0 - fetch statement was executed successfully
-1 - row that needs to be fetched is beyond the result set
-2 - row that needs to be fetched is missing
* FETCH_STATUS is defined globally for all the cursors on a connection, so when we are using it we need to be careful to check the status immediately after the fetch before another fetch occur.
* you can get the number of rows in the cursors result set using the @@CURSOR_ROWS variable

---(5)---
CLOSE myCursor
DEALLOCATE myCursor
* after using the cursor we must close and de-allocate it so there wont be any references for the cursor in the memory