Some Questions Answers:- What is the difference between a NULL pointer and a void pointer?

A NULL pointer is a pointer of any type whose value is zero. A void pointer is a pointer to an object of an unknown type, and is guaranteed to have enough bits to hold a pointer to any object. A void pointer is not guaranteed to have enough bits to point to a function (though in general practice it does)

What is encapsulation technique?

Hiding data within the class and making it available only through the methods. This technique is used to protect your class against accidental changes to fields, which might leave the class in an inconsistent state.

Definition of Object Oriented Programming in single line?

Object oriented programming is a programming paradigm which  uses objects and its interactions to design applications  and computer programs.

What is virtual function?

The virtual keyword means that method, property or function can be overridden

What’s a Windows process?

It’s an application that’s running and had been allocated memory.

What is programming?

Computer programming is writing or editing a computer program. A computer program is a set of instructions which determine how the computer will react to input when that program is running.

What is a debugger?

debugger is a program in which you run another program that you are trying to debug. Inside a debugger, you can step through your program one line or instruction at a time, set break points and have your program run until it hits one, examine the contents of variables and memory, and such other useful things as that.

what is a Programming language?

A programming language is a stylized communication technique intended to be used for controlling the behavior of a machine (often a computer). Like human languages programming languages have syntactic and semantic rules used to define meaning.

What's the difference between a programming language, a scripting language?

The main difference between a "programming language" (C, C++ etc.) and a "scripting language" (ASP, JSP, JavaScript, VBScript) is that code written in a programming language needs to be compiled before it is run. Once it is compiled, it can be run any number of times. Scripting languages, on the other hand, are interpreted at run-time. This means that every time you want to run the program, a separate program needs to read the code, interpret it, and then follow the instructions in the code. Compiled code has already been interpreted into machine language, so it is will typically execute faster because the conversion into machine language has already been done.

What is difference between overloading and overriding?

Same methods (Names are same) with different signature (parameters) is called overloading, while having same name and parameter functions in base and drive class called overriding.

What are the advantages of OOPS?

Advantages of OOPS are Re-usability, Maintainability, Extensibility, Modifiability, Modularity, Simplicity

What are the features of OOPS?

These are the main features of OOPS, a) Abstraction b) Encapsulation c) Inheritance d) Polymorphism

What is Class and Object

A Class is blueprint or a template to create an Object. Whereas an Object is a an actual instance of a Class.

Explain modeling and its advantages?

Modeling is a proven and well-accepted engineering technique which helps build a model. Model is a simplification of reality; it is a blueprint of the actual system that needs to be built.

What are the various types of Software Testing?

There are 7 different types of testing are done for a project, they are a) Unit Testing, b) Integration Testing, c) System Testing, d) Acceptance Testing, e) Alpha and Beta Testing, f) Black Box Testing and g) White Box Testing

What is ER Diagram

ER model is a conceptual data model that views the real world as entities and relationships. A basic component of the model is the Entity-Relationship diagram which is used to visually represents data objects.

Write a program to add two numbers without using arithmetic operator?

public static void main(String args[]) { int a=3,b=5; While(b--) a++; System.out.println("sum is"+a); }

Write a program to swap two numbers without using a temporary variable.

public static void main() { int a=4,b=5; a=a+b; //a=9 b=a-b; //b=4 a=a-b; //a=5 System.out.println("After swapping"+a,+b); }

Write a program to find largest of 2 numbers without using if-else

void main() { cin>>a>>b;; //let a=3and b=2 float c=|(a+b)|/2+|(a-b)|/2; //c=2.5+0.5=3.0 cout<<"largest number is"<<c; }

SQL Commands

Database

A database consists of one or more tables. A table is identified by its name. A table is made up of columns and rows. Columns contain the column name and data type. Rows contain the records or data for the columns.

Basic SQL

Each record has a unique identifier or primary key. SQL, which stands for Structured Query Language, is used to communicate with a database. Through SQL one can create and delete tables. Here are some commands:

• CREATE TABLE - creates a new database table
• ALTER TABLE - alters a database table
• DROP TABLE - deletes a database table
• CREATE INDEX - creates an index (search key)
• DROP INDEX - deletes an index

SQL also has syntax to update, insert, and delete records.

• SELECT - get data from a database table
• UPDATE - change data in a database table
• DELETE - remove data from a database table
• INSERT INTO - insert new data in a database table

SELECT

The SELECT is used to query the database and retrieve selected data that match the specific criteria that you specify:

SELECT column1 [, column2, ...]
FROM tablename
WHERE condition

The conditional clause can include these operators

• = Equal
• > Greater than
• < Less than
• >= Greater than or equal
• <= Less than or equal
• <> Not equal to
• LIKE pattern matching operator

SELECT * FROM tablename

returns all the data from the table.

Use single quotes around text values (most database systems will also accept double quotes). Numerical values should not be enclosed in quotes.

LIKE matches a pattern. The wildcard % is used to denote 0 or more characters.

• 'A%' : matches all strings that start with A
• '%a' : matches all strings that end with a
• '%a%' : matches all strings that contain an a

CREATE TABLE

The CREATE TABLE statement is used to create a new table. The format is:

CREATE TABLE tablename
(column1 data type,
column2 data type,
column3 data type); 

• char(size): Fixed length character string.
• varchar(size): Variable-length character string. Max size is specified in parenthesis.
• number(size): Number value with a max number of columns specified in parenthesis
• date: Date value
• number(size,d): A number with a maximum number of digits of "size" and a maximum number of "d" digits to the right of the decimal

INSERT VALUES

Once a table has been created data can be inserted using INSERT INTO command.

INSERT INTO tablename
(col1, ... , coln)
VALUES (val1, ... , valn) 

UPDATE

To change the data values in a pre existing table, the UPDATE command can be used.

UPDATE tablename
SET colX = valX [, colY = valY, ...]
WHERE condition 

DELETE

The DELETE command can be used to remove a record(s) from a table.

DELETE FROM tablename
WHERE condition

To delete all the records from a table without deleting the table do

DELETE * FROM tablename

DROP

To remove an entire table from the database use the DROP command.

DROP TABLE tablename 

ORDER BY

ORDER BY clause can order column name in either ascending (ASC) or descending (DESC) order.

ORDER BY col_name ASC

AND / OR

AND and OR can join two or more conditions in a WHERE clause. AND will return data when all the conditions are true. OR will return data when any one of the conditions is true.

IN

IN operator is used when you know the exact value you want to return for at least one of the columns

SELECT * FROM table_name WHERE col_name IN (val1, val2, ...)

BETWEEN / AND

The BETWEEN ... AND operator selects a range of data between two values. These values can be numbers, text, or dates.

SELECT * FROM table_name WHERE col_name BETWEEN val1 AND val2

JOIN

There are times when we need to collate data from two or more tables. That is called a join. Tables in a database are related to each other through their keys. We can associate data in various tables without repeating them. For example we could have a table called Customers which could have information about customers like their name, address, phone numbers. We could have another table called Products that has information regarding the products like part number, product name, manufacturer, number in stock, unit price. A third table called Orders could have information regarding what product was ordered, by whom, the date the order was placed, and quantity. Here are the tables:

Customers
Cust_ID	FirstName	LastName	Address	Phone
01	Mickey	Mouse	123 Gouda St.	456-7890
02	Donald	Duck	325 Eider Ln.	786-2365

Products
Part_No	Name	Manufacturer	In_Stock	Price
20-45	Hammer	Stanley	57	3.50
21-68	ScrewDriver	DeVries	84	2.75

Orders
Order_No	Part_No	Cust_ID	Date	Quantity
2005-27	21-68	02	31 Oct 2005	2
2005-34	20-45	01	02 Nov 2005	3

We can obtain information on who has ordered what:

SELECT Customers.FirstName, Customers.LastName, Products.Name
FROM Customers, Products, Orders
WHERE Customers.Cust_ID = Orders.Cust_ID AND Products.Part_No = Orders.Part_No 

We can select data from two tables with INNER JOIN. The INNER JOIN returns all rows from both tables where there is a match. If there are rows in Customers that do not have matches in Orders, those rows will not be listed.
SELECT Customers.FirstName, Customers.LastName, Orders.Date
FROM Customers
INNER JOIN Orders
ON Customers.Cust_ID = Orders.Cust_ID 

The LEFT JOIN returns all the rows from the first table (Customers), even if there are no matches in the second table (Orders). If there are rows in Customers that do not have matches in Orders, those rows also will be listed.
SELECT Customers.FirstName, Customers.LastName, Orders.Date
FROM Customers
LEFT JOIN Orders
ON Customers.Cust_ID = Orders.Cust_ID 

The RIGHT JOIN returns all the rows from the second table (Orders), even if there are no matches in the first table (Customers). If there had been any rows in Orders that did not have matches Customers, those rows also would have been listed.
SELECT Customers.FirstName, Customers.LastName, Orders.Date
FROM Customers
RIGHT JOIN Orders
ON Customers.Cust_ID = Orders.Cust_ID 

ALTER TABLE

With ALTER TABLE you can add or delete columns in an existing table. When you add a column you must specify a data type.
ALTER TABLE table_name
ADD col_name datatype

ALTER TABLE table_name
DROP COLUMN col_name 

UNION

The UNION command is used to select data from two tables very similar to the JOIN command. But the UNION command can be used only with columns having the same datatype. With UNION only distinct values are selected, i.e. if there are common data in the two tables only one instance of that data is returned.

SELECT Name FROM Customers_USA
UNION
SELECT Name FROM Customers_Asia

This will select all the customers from USA and Asia but if there is a name that occurs in both the tables it will return only one such name. To get all the names use UNION ALL instead.

SQL Functions

There are several built-in functins in SQL. The basic function types are:

• Aggregate Functions: These are functions that operate against a collection of values, but return a single value.
• Scalar Functions: These functions operate against a single value, and return a single value.

To use a built-in function the syntax is:

SELECT function (col_name) FROM table_name 

GROUP BY

The GROUP BY was added to SQL so that aggregate functions could return a result grouped by column values.

SELECT col_name, function (col_name) FROM table_name GROUP BY col_name 

HAVING keyword was introduced because the WHERE keyword could not be used. HAVING states a condition.

SELECT clo_name, function (col_name) FROM table_name
GROUP BY col_name
HAVING function (col_name) condition value 

CREATE VIEW

A view is a virtual table that is a result of SQL SELECT statement. A view contains fields from one or more real tables in the database. This virtual table can then be queried as if it were a real table.

CREATE VIEW view_name AS
SELECT col_name(s)
FROM table_name
WHERE condition

A view could be used from inside a query, a stored procedure, or from inside another view. You can add functions and joins to a view and present the data you want to the user.