Here, I tried to cover interfaces in my own words:

Interface

An interface is simply a collection of function prototypes. An Interface is a reference type like a class, but interface can contain only abstract members. In other words, Interface is a contract that defines the signature of the functionality.

An interface looks like a class definitions, but its only purpose is to define a set of methods and not to implement them. For this reason the interface definition includes only the definition of methods [in other words the abstract methods]. Interface contains only methods, properties and delegates but can not contain fields, constructors, destructor and any type of static members.

For more details and example refer to : http://gauravarora.indiamentor.com/Chapters/csharplanguageii.htm

Related posts:

1. What are Classes and structures
2. What is differance between Abstract and Interface
3. What are the good practices to use while designing for reuse

Structures

A structure in C# is simply a composite data type [you are well aware from composite data type, refer to data types for more details], which consists number of members of other types. The structure define simply by using the struct keyword.

eg. struct enroll
{
   public string name, fname, mname;
   public string char sex;
   Public int age;
   public string address;
}

Classes

It is cleared from above study that Classes are reference type. A class is a collection of its data members. Data members are those members of class which contains the data of class like fields, constants and events etc. Class is declared simply just followed by class keyword with optional modifiers; by default C# classes are public.

eg. class myClass
{
   public int xyz;
   public string name;
   public const int y=22;
}

Look into more details at : http://gauravarora.indiamentor.com/Chapters/csharplanguageii.htm

Related posts:

1. Can I inherit two difference classes to partial classes?
2. Is it possible to create constructor for an Abstract class?
3. How can I create a Singleton class by using public constructor?

Example:

Abstract class  myAbstClass

{

public myAbstClass()

{ }

private myAbstClass(int x)

{ //some implementation }

protected myAbstClass(string strX, string strY, int x)

{ //some implementation }

}

Related posts:

1. How can I create a Singleton class by using public constructor?
2. What is differance between Abstract and Interface
3. What are Classes and structures

Q. I have a following table :

I want results as :

Ans: At the time of interview I wasn’t easy with the answer but I wrote a query, but interviewer not satisfied.

I got the following proper query/solution from one of my colleagues Mr. sandeep Walia:

declare @tbl table(university varchar(100),Utotals int, status varchar(100),statuscnt int)

insert into @tbl(university,Utotals,status,statuscnt)

select ‘u1′,100,’pending’,20

union all

select ‘u1′,100,’Active’,20

union all

select ‘u1′,100,’Deferred’,60

union all

select ‘u2′,60,’pending’,20

union all

select ‘u2′,60,’Active’,20

union all

select ‘u2′,60,’Deferred’,20

select * from @tbl;

with cte as (

SELECT ROW_NUMBER() OVER(PARTITION BY university ORDER BY university DESC) AS RowID,

*

FROM @tbl

)

SELECT case when rowid=1 then university else null end university,case when rowid=1 then Utotals else null end Utotals,status,statuscnt

FROM cte

Related posts:

1. Create dynamic query with dynamic joins
2. Change date format mm/dd/yy to dd/mm/yy using query?
3. What is File Status in VSAM?

declare @tt table(col1 varchar(10), joinexp varchar(100))

insert into @tt

select ‘c1′,’join table2 on table1.id = table1.id’

union all

select ‘c2′,’join table3 on table2.id = table1.id’

union all

select ‘c3′,’join table4 on table3.id = table1.id’

union all

select ‘c4′,’join table5 on table5.id = table1.id’

union all

select ‘c5′,NULL

union all

select ‘c6′,NULL

declare @str varchar(1000)

set @str = ‘Select c1,c4,c5,c8,c9 from table1′

declare @tt table(col1 varchar(10), joinexp varchar(100))insert into @ttselect ‘c1′,’join table2 on table1.id = table1.id’union allselect ‘c2′,’join table3 on table2.id = table1.id’union allselect ‘c3′,’join table4 on table3.id = table1.id’union allselect ‘c4′,’join table5 on table5.id = table1.id’union allselect ‘c5′,NULLunion allselect ‘c6′,NULL
declare @str varchar(1000)set @str = ‘Select c1,c4,c5,c8,c9 from table1′

Now, in above create dynamic query with dynamic join with the subsequent column from C1,c4 etc.

Ans: Select @str = @str + space(1) + joinexp

from @tt

where CharIndex(col1,@str) > 0 and joinexp <>”

Select @str

Related posts:

1. Write query to get custom results
2. What is the syntax required for the creation of a cursor?
3. Change date format mm/dd/yy to dd/mm/yy using query?

I have two classes XYZ and ABC and two partial classes  of class myClass now is it possible:

partial class myClass : XYZ

{

}

partial class myClass : ABC

{

}

Ans:  This question I have asked in RSystems, Noida and I am sharing hereunder with you :

We can’t inherit two difference classes to partial class because in C# multiple inheritance is not possible using classes.

The main reason is in C# we cant do the following:

class myClass : XYZ, ABC

{

}

It will throw an error while we compile the code.

Related posts:

1. What are Classes and structures
2. When you inherit a protected-class-level variable,who is it available to?
3. Can we store filtered DataView in ViewState?

Related posts:

1. What is a view?
2. What is a tablespace?
3. What is a Declarations Generator (DCLGEN)?

declare @dt datetime

set @dt=’1/1/2010′ –Want to know January’s Last Monday Date

SELECT dateadd(d,-datepart(dw,DATEADD(d, -datepart(d,dateadd(mm,1,@dt)),dateadd(mm,1,@dt))-1)+1,DATEADD(d, -datepart(d,dateadd(mm,1,@dt)),dateadd(mm,1,@dt)))

Related posts:

1. Write query to get custom results
2. Change date format mm/dd/yy to dd/mm/yy using query?
3. Create dynamic query with dynamic joins

Can we create a singleton class using public constructor?

Simply answer is yes.

Practically, many of us aware that we can create a singleton class by using private constructor an creating a property, but we can create a singleton class by using public constructor as folows:

static void Main(string[] args)

{

try

{

Singleton obj3 = new Singleton2();

Singleton obj4 = new Singleton2();

Console.Read();

}

catch (Exception ex)

{

Console.WriteLine(ex.ToString());

Console.Read();

}

}

Related posts:

1. Is it possible to create constructor for an Abstract class?
2. Difference between Clone, Close and Dispose methods of Crystal Report?
3. Define Lambda expressions

Left side of this operator specifies the input parameters and contains the expression or statement block at the right side.

Example: myExp = myExp/10;

Now, let see how we can assign the above to a delegate and create an expression tree:

delegate int myDel(int intMyNum);
static void Main(string[] args)
{
//assign lambda expression to a delegate:
myDel myDelegate = myExp => myExp / 10;
int intRes = myDelegate(110);
Console.WriteLine("Output {0}", intRes);
Console.ReadLine();
//Create an expression tree type
//This needs System.Linq.Expressions
Expression<myDel> myExpDel = myExp => myExp /10;
}

Related posts:

1. What is a Lambda expression?
2. How can I create a Singleton class by using public constructor?
3. Difference between Clone, Close and Dispose methods of Crystal Report?