Switch Case,switch Statement in C#.NET

switch case or Switch statement

Switch statement is used to move the program control to a specific "Switch Case" based upon the Switch expression.

It can be used as a alternative to IF-ELSE.

Below is the skeleton for the Switch case .

switch (expression)  

{  

   case value-1:  

      Statement  

   break;  

   case value-2:  

      Statement  

   break;  

   case value-3:  

         Statement  

   break;  

   default:  

      Statement  

   break;  

}  

In the above , Expression can be any non null value . based upon the value of "Expression" the statement will be executed.

Lets Understand with a flow chart .

Flow Chart for Switch Statement,switch case

In the Above chart Enter a value to the switch statement Say "Age". Then switch Case will compare the "Age" value to the Case statement value and Print the statement. 

Before Writing the program lets understand the algorithm.

Step 1. Start

Step 2. Read Age

Step 3. Case 1:

            print "Your age is 1"

Step 4. Case 2:

            print "Your age is 2"

Step 5. Case 3:

            print "Your age is 3"

Step 6. Default:

            print "You are not a child"

Step 7. End

Lets Convert above chart and Algorithm to a Program and check the output.

using System;

namespace Console-Application

{

    class Switch-Check

    {

        public static void Main()

        {

            int iAge = 0;

            Console.WriteLine("Enter a number....");

            iAge = Convert.ToInt16(Console.ReadLine());

            switch (iAge)

            {

                case 1:

                    Console.WriteLine("Your Age is " + iAge);

                    break;

                case 2:

                    Console.WriteLine("Your Age is " + iAge);

                    break;

                case 3:

                    Console.WriteLine("Your Age is " + iAge);

                    break;

                default:

                    Console.WriteLine("Your are not a child");

                    break;

            }

            Console.ReadKey();

        }

    }

}

Output

See above output after running the above program in the visual studio.

In first output our entered value matches the Case statement so it printed the statement.
In second output our entered value did not matches the Case statement so it printed the statement which is Default one.

Few Points Need to Know about switch statement

1.It checks only the match "Case" equal to switch statement value and show the output rather than check each "Switch Case" unlike if-else.

2.It uses Jump table which makes Switch statement faster over if-else.

3.When conditions becomes very long in a program then we should prefer Switch over if-else.

Thanks.............

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Understand Conditional Statement in C#

Introduction

Conditional statement is a set of Rule performed if a certain Condition met.
We can achieve this using IF-ELSE Statement.

Skeleton of IF-ELSE Statement

if(<condition-1>)
{
      print message
}
else if(<condition-2>)
{
      print message
}
else
{
     print message

}

we can use only IF instead of IF-ELSE Statement as below.

if(<condition-1>)
{
      print message
}
if(<condition-2>)
{
      print message
}
if(<condition-3>)
{
     print message

}

flowchart for if-else statement

The above chart describe as below algorithm.

Step 1. Start

Step 2. Read two number a,b

Step 3. if(a>b) then 

            print " a is greater"

Step 4. else if(a=b) then 

             print "Both are same"

Step 5. else(a>b) then 

             print " b is greater"

Step 6. End

Lets Convert this algorithm to a C# program.

using System;

namespace ConsoleApp1

{

    class ifelsecheck

    {

        public void CheckIfElse()

        {

            int a, b = 0;

            Console.WriteLine("Enter two number..");

            a = Convert.ToInt16(Console.ReadLine());

            b = Convert.ToInt16(Console.ReadLine());

            if (a > b)

                Console.WriteLine(a + " is bigger");

            else if (a == b)

                Console.WriteLine(a + " and " + b + " are equal");

            else

                Console.WriteLine(b + " is bigger");

            Console.ReadKey();

        }

    }

}

Limitations

• IF-ELSE check each and every condition till the condition is satisfied.
• Performance will degrade if more condition is there in the statement.
• ELSE is optional  in the statement but IF is compulsory to use it.
• The difference between IF and IF-ELSE is as below.
• IF will check each and every condition 
• IF-ELSE will check till condition satisfied.

Thanks.......

t.

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Introduction To C# with an Example

Introduction to c#

C#  is a high level language and its first version C# 1.0  released by Microsoft in 13th February 2002. Syntax is almost similar to C++.

what is c#?

• C# is an Object Oriented Programming Language Developed By Microsoft.
• C# is a high level Language as this does not depend upon the hardware directly.
• Users having good knowledge into C++ can use it as syntax is almost similar to C# .

Why C#?

Below are the reason why C# is more popular.

• Easy to Start- As C# syntax is similar to C,C++ and Java , Developer can easily migrate to this language and learn with no time.

• Widely used in Desktop and Web Application-As C# is more popular because of easy syntax and reach library, this is used widely now a days

• Larger Community-C# has larger community and hence more IDE to develop program.

• Game Development- C# is more popular in Game development because of reach libraries and easy to develop.

c# compare version numbers                                                           

Version number CLR version Release date
1.0 1.0 2002-02-13
1.1 1.1 2003-04-24
2.0 2.0 2005-11-07
3.0 2.0 2006-11-06
3.5 2.0 2007-11-19
4.0 4 2010-04-12
4.5 4 2012-08-15
4.5.1 4 2013-10-17
4.5.2 4 2014-05-05
4.6 4 2015-07-20
4.6.1 4 2015-11-17
4.6.2 4 2016-08-02
4.7 4 2017-04-05
4.7.1 4 2017-10-17


Lets Understand with a program.

Open/Lunch Visual Studio-> Go to File->New->Project

New Project Pop up will Appear.

Under Templates Select Visual C# and select the template 

called Console App as below.

visual studio application templates

Enter Project Name and Solution name of your Choice.

Set the location for your project and Click OK as below.

project and solution visual studio

A new project will be created based upon the Project name and the solution name.

Lets Write a simple program under above created Project.

using System;

namespace ConsoleApp1
{
    class SampleProgram
    {
        //Read Technotech
        //Print Welcome to Technotech
        static void Main(string[] args)
        {
            String string1 = string.Empty;
            Console.WriteLine("Enter a String....");
            string1 = Console.ReadLine();
            Console.WriteLine("Welcome to " + string1);
            Console.ReadKey();
        }
    }
}

Press F5 or Ctrl + F5 to run the application.

console output c#

In the above Image I enter "Technotech"
We got the output "Welcome to Technotech"


Thanks..........

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difference between where and having clause in sql server

Introduction

Both Where and and having clause used to filter the record but for different purpose.

Lets Get Started

Where clause used to filter the data by row where as Having clause  is used to filter based upon the aggregate data.

Lets Understand practically.

I created a table as TEST-INSERT and inserted some value to it as below.

CREATE TABLE [TEST-INSERT]

( [RNO] [int] NULL, [ID] [int] NULL, [NAME] [varchar](20) NULL, [Category] [varchar](50) NULL) 

INSERT INTO TEST-INSERT VALUES(1,1,'Mark','Teacher')

INSERT INTO TEST-INSERT VALUES(2,2,'Ben','Teacher')

INSERT INTO TEST-INSERT VALUES(3,3,'Paul','Student')

INSERT INTO TEST-INSERT VALUES(4,4,'Struat','Student')

INSERT INTO TEST-INSERT VALUES(5,5,'RK','Cleark')

Table will display like below.

RNO         ID          NAME                 Category

----------- ----------- -------------------- --------------

1           1           Mark                 Teacher

2           2           Ben                  Teacher

3           3           Paul                 Student

4           4           Struat               Student

5           5           RK                   Cleark

Difference-1

If we want to select some specific row then we can use where clause as shown below.

SELECT * FROM TEST-INSERT WHERE ID=2 

If we want to count based up on the category then we can use Having clause.
See below query.

SELECT Category,COUNT(1) "Teacher Count" FROM TEST-INSERT GROUP BY Category HAVING Category='Teacher'

Difference-2

We can use where clause in Update query where as we can not use Having clause in Update query.

UPDATE TEST-INSERT SET Category='Student' WHERE ID=5

Difference-3

We we are using Having clause then Group by must be there in the query but in case of where no need any clause .

Difference-4

If we want to search any record from the table then we should go for Where clause.

If we are checking the duplicate record in a table or checking the count of a record based upon category we should go for Having clause.

Interview questions and Answers

1. Can we use Where and Having clause in a same table?

Yes,We can . See the below query.

SELECT Category FROM TEST-INSERT WHERE Category in('Student','Teacher') GROUP BY Category HAVING Category='TEACHER'

2. How to check the duplicate record from a table?

SELECT Category,COUNT(1) "Teacher Count" FROM TEST-INSERT GROUP BY Category HAVING COUNT(Category)>1

The above query will count the duplicate record whose count is more than 1.

2. Can we write Having Clause without Group By?

No,Not Possible.

Thanks.....................

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Difference between Union and Union All

Introduction

Both Union and Union All are Used to Join Rows of two or more tables.

But the Union Or Union All  need the datatype same .

Lets Understand with the below example.

Difference-1

Union 

Union will combine table rows and will display the non repeated records, which are not duplicate.

See the below query and see the below output.

Query

select 'India'

union

select 'Pakistan'

union

select 'Australia'

union

select 'Pakistan'

union

select 'India'

Output

Australia

India

Pakistan

Union All

1.Union All will combine table rows and will display all records .

See the below query and see the below output.

Query

select 'India'

union all

select 'Pakistan'

union all

select 'Australia'

union all

select 'Pakistan'

union all

select 'India'

Output

India

Pakistan

Australia

Pakistan

India

You can see India and Pakistan repeated in Both the query but we get different result.

Difference-2

Union Use sort mechanism based upon its key while displaying the record where as Union All never use sort mechanism. It display the record as it is .

Lets Take an example .

Let create two table as below.

create table tblUnion1

(

id int,

Name varchar(20),

Country varchar(20)

)

create table tblUnion2

(

id int,

Name varchar(20),

Country varchar(20)

)

Lets Insert few records to both the tables as below.

insert into tblUnion1 values(1,'Name1','India')

insert into tblUnion1 values(2,'Name2','Pakistan')

insert into tblUnion1 values(3,'Name3','Australia')

insert into tblUnion2 values(1,'Name1','India')

insert into tblUnion2 values(2,'Name2','Pakistan')

insert into tblUnion2 values(3,'Name3','Australia')

insert into tblUnion2 values(5,'Name5','Australia')

insert into tblUnion2 values(4,'Name4','Srilanka')

Lets Execute the below query using UNION and UNION ALL and see what is going to happen.

select * from tblUnion1

union

select * from tblUnion2

Output for Union

1 Name1 India

2 Name2 Pakistan

3 Name3 Australia

4 Name4 Srilanka

5 Name5 Australia

select * from tblUnion1

union all

select * from tblUnion2

Output For Union All

1 Name1 India

2 Name2 Pakistan

3 Name3 Australia

1 Name1 India

2 Name2 Pakistan

3 Name3 Australia

5 Name5 Australia

4 Name4 Srilanka

See the above two output .

In Case of Union we got the data in a sorted order where in case of Union All we got the data as it is in the table.

Difference-3

Lets check the performance.

To check performance we can use Execution Plan for both Union and Union All.

To get execution plan along with the output you can goto Query->Include Actual Execute Plan

See the below Image.

Execution Plan Option

After Inclusion of execution Plan Lets execute the Below statements and see the execution Plan associated with it.

select * from tblUnion1

union

select * from tblUnion2

Execution Plan for Union

select * from tblUnion1

Union All

select * from tblUnion2

Execution Plan for Union All

See Both the Execution Plan. 

In 1st case(UNION) the execution plan taking 63% for sorting where as in 2nd case(UNION ALL) the execution do not have any sorting operation.

So this conclude that UNION ALL is faster than UNION.

Note

Lets note some point what we discussed above.

1. Union take Unique records where as Union All take all the records whether it is repeated or non repeated.
2. Union All is faster than Union as Union take extra time while sorting the record.
3. When we need unique records we use Union.
4. When we need duplicate records also then we will use Union All.
5. It is recommended to use Union All as much as possible compared to Union because of the better performance prospective.

For More Information Please refer below books....

Thanks........... 

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Dynamic SQL Query in SQL Server and Why We Need This

Introduction

Before Dive into the Topic of Dynamic SQL query lets have a look into Static query and why we need dynamic SQL query even though we have Static query .
Lets Get Started....
See the below Image which describes the SQL Queries types based upon the execution.
Basically we will discuss more about Dynamic SQL rather than Static SQL.

SQL Queries

It can be divided into 2 types.

• Static SQL Query

• Dynamic SQL query

Static SQL Query

Static SQL query is known at compile time i.e. Compiler have the idea about the SQL query .
This is straight forward what we use our day to day life. See the below example.

SELECT * FROM TESTINSERT t WHERE t.NAME='Rahul'

We are not warping the SQL Query as a string.  

Dynamic SQL query

Dynamic SQL query is not known at compile time i.e. Compiler do not have any idea about the SQL query .
This is quite different than the normal SQL Statement as this can not be executed straight forward.
This dynamic SQL query wrap in a string format and get executed by using below commands.

• EXECUTE(<string value>)

• EXECUTE SP_EXECUTESQL(<string value>)

We will discuss the above two command this article.Lets discuss Dynamic SQL with an example.

DECLARE @Statement NVARCHAR(200)DECLARE @Name VARCHAR(10)

SET @Statement ='SELECT * FROM TESTINSERT t WHERE t.NAME=''' + @Name''''EXECUTE(@Statement )

The above is the example of Dynamic SQL as it stored in a string variable called @Statement and in the next step it execute the string to get the output by using EXECUTE Command.

Lets Dig into the Topic and Understand the topic more deeper.

1. EXECUTE SP_EXECUTESQL,<SQLstring>, <datatype>,parametervalue
2. EXECUTE(<SQL String>)

Lets Understand the below example.

Procedure-1(Execute)

--EXECUTE [PROCDynamicQueryExecute]
ALTER PROCEDURE [dbo].[PROCDynamicQueryExecute]
  AS
  BEGIN
  DECLARE @ID INT
  SET @ID=1
  DECLARE @FullQuery NVARCHAR(500)
  SET @FullQuery = N'SELECT * FROM TESTINSERT WHERE id= ' + CAST(@ID AS                VARCHAR) EXECUTE(@FullQuery)
END

Procedure-2  (Execute sp_executesql)

--EXEC [PROCDynamicQuery_ExecuteSQL]

ALTER PROCEDURE [dbo].[PROCDynamicQuery_ExecuteSQL]

AS

BEGIN

DECLARE @ID INT

SET @ID=1

DECLARE @QryName NVARCHAR(100)

set @QryName=N'ID=@ID'

DECLARE @str Nvarchar(100)

SET @str = N'@ID INT'

DECLARE @FullQuery NVARCHAR(500)

SET @FullQuery = N'SELECT * FROM TESTINSERT WHERE id= @ID'

EXECUTE sp_Executesql @FullQuery,@str,@ID=1

END

See the two procedure(Procedure1 and Procedure2) Carefully and lets find the difference between these two.

Difference 1

In Procedure1 we can not pass the value to the Execute(not allow parameter) where as we can pass the value in Procedure2(parameterized). See the below command.

1. EXECUTE(@FullQuery)
2. EXECUTE sp_Executesql @FullQuery,@str,@ID=1

Difference 2

We  can apply Execute Sp_ExecuteSQL in place of Execute .

Example- EXECUTE sp_Executesql @FullQuery

Difference 3

Risk of SQL injection is more in case of Execute where as less in Execute SP_executesql.

Difference 4

Plan not cached in Execute where as Plan cached in Execute SP_executesql. at 1st execution.

Note

Both the dynamic query building technique helps to build the dynamic SQL. So that even if we do not have any idea about the value in compile time we can can execute the query using Dynamic SQL with the help of the 2 command above discussed. We normally use dynamic query when value is known at run time.

Thanks.....................................

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