List of Frequently asked Interview Questions for C#.Net

1) What is .net framework?

2) What is abstract class?

3) What is Interface?

4) How does abstract class differ from Interface?

5) What is monitor object?

6) What will happen if any UI element is being updated by background thread in winform based multi-threaded application?

7) What are delegates?

8) Difference between DataReader and DataAdapter?

9) What is Garbage collector?

10) How does garbage collector work?

11) What is different between private and sealed class?

12) What is use of finally block?

13) How can you implement Singleton Design Pattern in C# code?

Abstract Class v/s Interface

Introduction 

In this article I will discuss Interfaces versus Abstract classes. The concept of Abstract classes and Interfaces is a bit confusing for beginners of Object Oriented programming. Therefore, I am trying to discuss the theoretical aspects of both the concepts and compare their usage. And finally I will demonstrate how to use them with C#.

What is an Abstract Class?

How to create Extension methods for predefined datatype in JavaScript

In Javascript one can create extension(for eg: for string it can be obj.Trim(), obj.LTrim(), obj.RTrim etc) methods for predefined data types. These kind of methods can be created by using prototype property of datatypes.
Here In below code I am showing Extension methods for String DataType.

<script type="text/javascript" language="javascript">
        String.prototype.LCase = function () { return this.toLowerCase(); }
        String.prototype.Trim = function() { return [Some PROCESSED VALUE];}
    </script>

Now as we have written Two extension methods for string data types and suppose we have string variable called str  then we can use these methods like str.LCase(), str.Trim(). 

LINQ to Object (Load Dictionary/HashTable from DataTable)

Code to load data of DataTable in the Dictionary object (Considering there atleast one column which is containing unique values).

Consider a dictionary dicDetail which is to be loaded by the values available in a data table. I am considering that a table dtSample is containing 2 columns(RollNo, Name). Now our task is to load the data in the dictionary dicDetail. In which RollNo will be key and Name will be value.

LINQ to OBJECT(HashTable)

Scenario:

A detail class(Marks), which contains Object of a Structure(MarkDetails) as Data Member. There are some member functions like AddorUpdateRecord which is use to update data.

Another class named "MarksInfo" containing HashTable. The HashTable contains the object of class "Marks" as value fields and some key, (Hashtable will have one entry per student).

Requirement: We need to make DataTable that contains marks of all the students.

SQL Practice paper-1

Use tables given below for answering the questions

1. Person_info : Contains person’s information

Field Name	Width	Constraint	Description
person_id	Number(6)	Primary Key	Id of the person
person_name	Varchar2(20)	Not Null	Name of the person
address	Varchar2(35)		Address of the person
Phone_num	Number(10)		Phone number of the person

2. Car_info : Contains car’s information.

Field Name	Width	Constraint	Description
car_id	Number(4)	Primary Key	Id of the car
Make_yr	Number(4)	Not Null	Year of manufacturing of the car
model	Varchar2(35)	Not Null	Model of the car

3. Own_info: Contains person and its car information.

Field Name	Width	Constraint	Description
person_id	Number(6)	Foreign key	Id of the person
Car_id	Number(4)	Foreign key	Id of the car
Driver_name	Varchar2(20)	Not null	Driver name

4. Accident : Contains accident’s information of a car

Field Name	Width	Constraint	Description
Car_id	Number(4)	Primary key	Id of the car
Acc_date	Date	Primary Key	Date of the accident
Damage_amt	Number(6)		Damage amount

Car_id and acc_date is composite primary key

Q1.  Display the car id and date of accident in the day, month, and yyyy format.

Q2. Display the person id, person name, car id, year of make and model of all

       Person where year of manufacturing of a car is less than 2005

Q3. Display the person's name and the number of cars owned by that person

Q4.  There could be many cars of a specific model. Display each model with the number of cars of that model and the number of people who own that specific model. A person may own multiple cars of the same model.

SQL Practice paper-2

Use tables given below for answering the questions

Tables -

1. Person : Contains person’s information

Field Name	Width	Constraint	Description
person_id	Number(6)	Primary Key	Id of the person
person_name	Varchar2(20)	Not Null	Name of the person
Address	Varchar2(35)		Address of the person
Phone_num	Number(10)		Phone number of the person

2. Cars : Contains car’s information.

Field Name	Width	Constraint	Description
car_id	Number(4)	Primary Key	Id of the car
Make_yr	Number(4)	Not Null	Year of manufacturing of the car
Model	Varchar2(35)	Not Null	Model of the car

3. Owns: Contains person and its car information.

Field Name	Width	Constraint	Description
person_id	Number(6)	Foreign key	Id of the person
Car_id	Number(4)	Foreign key	Id of the car
Driver_name	Varchar2(20)	Not null	Driver name

4. Accident : Contains accident’s information of a car

Field Name	Width	Constraint	Description
Car_id	Number(4)	Primary key	Id of the car
Acc_Date	Date	Primary Key	Date of the accident
Damage_amt	Number(6)		Damage amount

Car_id and acc_date is composite primary key

Q1. Display the total damage amount of accidents up to 31-dec-2006

Q2. Display the car id, model, person name, acc_date, damage_amt

        Where accident occurred in the year 2005

Q3. Display model and no.of accident of that model for each year

Q4.  There could be many accidents of a specific model. Display each model

With the number of accidents of that model where the damage amount is more

Than 20,000

SQL Practice paper-3

Use tables given below for answering the questions

Tables -

1. Customer : Contains customer’s information who rent a property

Field Name	Width	Constraint	Description
Cust_id	Number(6)	Primary Key	Id of the customer
Cust_name	Varchar2(20)	Not Null	Name of the customer
Address	Varchar2(35)		Address of the customer
Phone_num	Number(10)	Not Null	Phone number of the customer

2. Property : Contains properties information

Field Name	Width	Constraint	Description
Property _id	Number(6)	Primary Key	Id of the Property
paddress	Varchar2(35)		Address of the property
rent	Number(5)		Rent of the property
Owner_id	Number(6)	Foreign key	Id of the owner

3. Owner : Contains owners  information

Field Name	Width	Constraint	Description
Owner_id	Number(6)	Primary Key	Id of the owner
Owner_name	Varchar2(20)	Not Null	Name of the owner
Owner_address	Varchar2(35)		Address of the owner
Own_ph_no	Number(10)		Phone number of the owner

4. Cust_property: Stores the information about properties taken on rent

Field Name	Width	Constraint	Description
cust_id	Number(6)	Foreign key	Id of the customer
Property _id	Number(6)	Foreign key	Id of the property
Rent_start	date		Date on which rent started
Rent_finish	date		Date on which rent finished

Q1. Display the average rent.

Q2. Display customer name, property address, rent, rent_start, and rent_finish of all

       Customers

Q3. Display the owner name and no.of properties owned by the owner

Q4. Display property address and number of customers lived in that property.

       The property rent should be more than Rs.5000