The application stays connected to the DB system even when it is not using DB services. This commonly wastes valuable and expensive database resources, as most of the time applications only query and view the persistent data. ADO.Net solves this problem by managing a local buffer of persistent data called data set. Our application automatically connects to the database server when it needs to run a query and then disconnects immediately after getting the result back and storing it in the dataset. This design of ADO.Net is called disconnected data architecture and is very much similar to the connectionless services of HTTP on the internet. ADO.Net also provides connection oriented traditional data access services. An important aspect of disconnected architecture is that it maintains a local repository of data in the dataset object. The dataset object stores the tables, their relationship and their different constraints. The user can perform operations like update, insert and delete on this dataset locally, and the changes made to the dataset are applied to the actual database as a batch when needed. This greatly reduces network traffic and results in better performance.
o We have been introduced to the concepts of objects and their various properties and methods. These inter-related concepts allow any web page to be broken down into little snippets of information or data, which can then be accessed by JavaScript and, in many cases, changed.
o However, what if we want to create our own storage space for information that doesn’t necessarily have a page-based counterpart? For example, what if we wanted to store the previous value of a document’s title property before changing it, so it could be retrieved later, or if we wished to store the date time that the page was loaded into the browser for reproduction in several places on the page, and didn’t want to have to recalculate the time on each occasion?
o Variables are named containers for values within JavaScript. They are similar to object properties in many ways, but differ importantly:
o In a practical sense, variables have no “parent” object with which they are associated.
o Variables can be created (“declared”) by you as a developer, and can be given any arbitrary name (within certain rules) – object properties, however, are restricted by the definition of the parent object. It would make no sense, for example, for our piano object in the previous chapters to have a propeller property!
Variable name rules are straightforward – no spaces, names must start with a letter. Examples of valid variable names are:
BrowserName
page_name
Message1
MESSAGE1
o In many browsers, JavaScript is case-sensitive, which means that the last two variables in the example above are distinct variables. It is a good idea to pick a particular naming style for your variables, and to stick to it within your projects.
o At the simplest level, variables can store three different types of value:
o Numbers
e.g. 1.3324, 3.14159, 100000, -8 etc.
o Strings
e.g. “JavaScript for Beginners, week 3”, “Hello World” etc.
o Boolean Values
e.g. true, false
o Note that strings can contain numbers, but the following variable values are not equivalent:
1.234 and “1.234”
The latter is a string value. This becomes important. Consider:
1+2 = 3
“a” + “b” = “ab”
“1” + “2” = “12”
o Some developers use their own naming convention with variable names to denote the type of value expected to be contained in a given variable. This can often be helpful, but is in no way required by JavaScript (c.f. JavaScript comments)
o For example, strMessage might indicate a string variable, where numPageHits might indicate a numerical value in the variable.
Variable assignment is accomplished in the same way as object property assignment. When a variable is assigned a value for the first time, it is automatically created. This is different from other programming languages, where a variable must be created explicitly first, before it can be loaded with a value.
o Some examples of variable assignment follow:
numBrowserVersion = 5.5;
numTotal += 33;
Message = “Hello!”;
Message = “Goodbye”; Message = 3;
o Note that the last three examples show that variable values can be altered after their initial assignment, and also that the type of value stored in a variable can be altered in a similar manner.
o Once a variable has been created and a value stored within, we will want to be able to access it and perhaps manipulate it. In a similar manner to object properties, we access our variables simply by calling them:
Message = “Hello World!”; alert(Message);
o Note that we do not use quote marks around our variable names. The above code is different from:
alert(“Message”);
for hopefully obvious reasons.
o As well as using variables for storage and access, we can combine and manipulate them using operators. For example:
a = 12; b = 13; c = a + b; // c is now 25 c += a; // c is now 37
c = b + “ Hello!”; // c is now “13 Hello!”
Our last example may have been unexpected – we added a number to a string and got a string as a result. JavaScript is smart enough to realise that a number cannot be “added” to a string in a numerical sense, so it converts the number temporarily to a string and performs a concatenation of the two strings. Note that b remains 13, not “13”. o A table of operators:
Operator
Function
x + y
Adds x to y if both are numerical – otherwise performs concatenation
x – y
Subtracts x from y if both are numerical
x * y
Multiplies x and y
x / y
Divides x by y
x % y
Divides x by y, and returns the remainder
-x
Reverses the sign of x
x++
Adds 1 to x AFTER any associated assignment
++x
Adds 1 to x BEFORE any associated assignment
x–
Subtracts 1 from x AFTER any associated assignment
–x
Subtracts 1 from x BEFORE any associated assignment
Project
o Open your previous project file, and save it under the name chapter_11.html.
o Clear the previous JavaScript code, and ensure that the script tags are contained in the body section of the document.
o Assign the message
“Welcome to my web site”
to a variable called greeting.
o Use this variable to create an alert box containing the message, and also to produce a header on the page without having to retype the message.
o Test this page in your browser.o Now, modify your code to create two variables, var_1 and var_2.
o Assign the value “Welcome to” to var_1, and the value “my web site” to var_2.
o Create a third variable var_3, and assign to it the value of var_1 + var_2. Then use an alert box to check the resultant value of var_3.
o A programming language is a set of codes that we can use to give a computer instructions to follow.
o Popular and well-known programming languages include Java, C++, COBOL, BASIC, LISP and more. Most popular programming languages consist of words and phrases that are similar in form to the English language.
o A well-written program will be easily readable by anyone with a little programming experience, regardless of whether they have any direct experience of the language in question. This is because modern programming languages share a large number of common concepts. In particular, they all have a notion of variables, arrays, loops, conditionals, and functions. We will meet these concepts again in more depth later in the course.
o Traditionally, programming languages have been used to write (for the most part) “stand-alone” applications. Things like Microsoft Word, Mozilla Firefox and Lotus Notes are all examples of such applications. Once installed on a PC, these applications run without necessarily requiring any other software to be installed alongside them.
o Web Applications differ from these traditional applications in many respects, but the most striking is that they all run inside your web browser. Examples of popular web applications are things like Google, Hotmail, Flickr, GMail and any of the vast array of “weblogging” systems.
o These applications are also written using programming languages, but as a rule they are built using multiple, interdependent technologies. These technologies are easily (though not completely) broken down into two categories: server-side and client-side.
o A programming language is a set of codes that we can use to give a computer instructions to follow.
o Popular and well-known programming languages include Java, C++, COBOL, BASIC, LISP and more. Most popular programming languages consist of words and phrases that are similar in form to the English language.
o A well-written program will be easily readable by anyone with a little programming experience, regardless of whether they have any direct experience of the language in question. This is because modern programming languages share a large number of common concepts. In particular, they all have a notion of variables, arrays, loops, conditionals, and functions. We will meet these concepts again in more depth later in the course.
o Traditionally, programming languages have been used to write
(for the most part) “stand-alone” applications. Things like Microsoft Word, Mozilla Firefox and Lotus Notes are all examples of such applications. Once installed on a PC, these applications run without necessarily requiring any other software to be installed alongside them.
o Web Applications differ from these traditional applications in many respects, but the most striking is that they all run inside your web browser. Examples of popular web applications are things like Google, Hotmail, Flickr, GMail and any of the vast array of “weblogging” systems.
o These applications are also written using programming languages, but as a rule they are built using multiple, interdependent technologies. These technologies are easily (though not completely) broken down into two categories: server-side and client-side.
o The World Wide Web is built on a number of different technologies.
o For most users, the web starts and ends with their choice of web browser. The browser is said to define the client-sideof the web, with the browser, the computer it is running on, and the user surfing the web being collectively referred to as the client.
o Consider a client who has decided to visit the web site at www.google.com. The first thing that happens is that the client will make a request to Google’s web server for the default page of that web site.
o The web server is an application running on a computer owned by Google. Like the client, the server application and the computer on which it runs define the server-side of the web, and are collectively referred to as the server.
o When the server receives the request from the client for a particular page, its job is to retrieve the page from the computer’s files and serve it back to the client. In many cases, this operation is a very simple procedure involving little or no work on the part of the server.
o However, using a programming language like PHP, Perl or Java, we can cause the server to either modify the page it finds before it passes it back to the client, or even to generate the page entirely from scratch. This is referred to as a server-side application. The page passed back to the client looks (to the client) exactly the same as any other page that has not been modified.
o An example of a server-side application might be to insert the current date and time into a page. This would mean that each time the page was requested (say, by using the browser’s refresh button), a new time value would be added to the page.
o Once the client has received the page from the server, it displays the page and waits for the user to request another page. As soon as the page reaches this state, it has moved beyond the control of the server. No server-side application can now alter the contents of the page without the client having to make another trip back to the server to get a new (and possibly updated) copy of the page.
o However, all modern browsers allow for the running of clientside applications. These are small applications which are embedded within the HTML code of the page itself.
o Server-side applications ignore any client-side applications that they find while modifying pages to send to the client, so in general the two types of application cannot easily “talk” to each other.
o However, once the client has received a client-side application, it can begin to modify the page dynamically, without the need to go back to the server.
o An example of a client-side application might be a clock on a web page that updated every second.
o An unfortunate side effect of client-side applications is that all the code must be sent to the client for running, which means that the application’s inner workings are available for anyone to see. This makes it impractical for checking passwords, or doing anything else that could cause confidential information to be released into the wild.
o In addition, all modern web browsers afford the user the opportunity to switch off client-side applications altogether. On top of this, the way the same client-side application is run will vary from browser type to browser type.
o Despite these drawbacks, client-side applications (or scripts, as they are better known due to their general brevity) remain the best way to provide web users with a rich environment when developing web applications.
o In short, the two technologies each have their strengths and weaknesses:
o Client-side scripts allow the developer to alter pages dynamically, and to respond to user actions immediately rather than having to wait for the server to create a new version of the page. However, there are security and cross-browser compatibility issues to be aware of, and these are often nontrivial.
o Server-side applications allow the developer to keep her code secure and secret, thus allowing for more powerful applications to be created. In addition, since the server running the code is always a known quantity, applications that run successfully in one browser will run successfully in all browsers. However, despite all this power, there is no direct way for a server-side application to alter a page without having to force the client-side to load another page. This makes it completely impractical for things like drop-down menus, pre-submission form checking, timers, warning alerts and so forth.
JavaScript is a client side programming language used to add programming logic to web pages.
Brendan Eich (born July 4, 1961) is an American technologist and creator of the JavaScript programming language. He co-founded the Mozilla project,[2] the Mozilla Foundation and the Mozilla Corporation, and served as the Mozilla Corporation’s chief technical officer and briefly, as its chief executive officer.[3] He is the CEO of Brave Software.[4] For more(Wikipedia.org)
Applications of JavaScript :-
Client side valiadtion
Helps in manipulating HTML pages
User Notification (Pop-ups in website)
Back-end Data Loading (Ajax library)
Presentations (RevealJs and BespokeJs)
Server Applications (NodeJs)
There are many useful Javascript libraries available:-
C operators are symbols that are used to perform mathematical or logical manipulations. The C programming language is rich with built-in operators. Operators take part in a program for manipulating data and variables and form a part of the mathematical or logical expressions.
Types of operators:-
C programming language offers various types of operators having different functioning capabilities.
Arithmetic Operators
Relational Operators
Logical Operators
Assignment Operators
Increment and Decrement Operators
Conditional Operator
Bitwise Operators
Special Operators
Arithmetic Operators:-
C supports all the basic arithmetic operators. The following table shows all the basic arithmetic operators.
Operator
Description
+
adds two operands
–
subtract second operands from first
*
multiply two operand
/
divide numerator by denominator
%
remainder of division
++
Increment operator – increases integer value by one
—
Decrement operator – decreases integer value by one
Relational operators:-
The following table shows all relation operators supported by C.
Operator
Description
==
Check if two operand are equal
!=
Check if two operand are not equal.
>
Check if operand on the left is greater than operand on the right
<
Check operand on the left is smaller than right operand
>=
check left operand is greater than or equal to right operand
<=
Check if operand on left is smaller than or equal to right operand
Logical operators:-
C language supports following 3 logical operators. Suppose a = 1 and b = 0,
Operator
Description
Example
&&
Logical AND
(a && b) is false
||
Logical OR
(a || b) is true
!
Logical NOT
(!a) is false
Bitwise operators:-
Bitwise operators perform manipulations of data at bit level. These operators also perform shifting of bits from right to left. Bitwise operators are not applied to float or double(These are datatypes, we will learn about them in the next tutorial).
Operator
Description
&
Bitwise AND
|
Bitwise OR
^
Bitwise exclusive OR
<<
left shift
>>
right shift
Assignment Operators:-
Assignment operators supported by C language are as follows.
Operator
Description
Example
=
assigns values from right side operands to left side operand
a=b
+=
adds right operand to the left operand and assign the result to left
a+=b is same as a=a+b
-=
subtracts right operand from the left operand and assign the result to left operand
a-=b is same as a=a-b
*=
mutiply left operand with the right operand and assign the result to left operand
a*=b is same as a=a*b
/=
divides left operand with the right operand and assign the result to left operand
a/=b is same as a=a/b
%=
calculate modulus using two operands and assign the result to left operand
a%=b is same as a=a%b
Conditional operator:-
The Conditional Operator in C, also called a Ternary operator, is one of the Operators, which used in the decision-making process. The C Programming Conditional Operator returns the statement depends upon the given expression result.
C operators are symbols that are used to perform mathematical or logical manipulations. The C programming language is rich with built-in operators. Operators take part in a program for manipulating data and variables and form a part of the mathematical or logical expressions.
Types of operators:-
C programming language offers various types of operators having different functioning capabilities.
Arithmetic Operators
Relational Operators
Logical Operators
Assignment Operators
Increment and Decrement Operators
Conditional Operator
Bitwise Operators
Special Operators
Arithmetic Operators:-
C supports all the basic arithmetic operators. The following table shows all the basic arithmetic operators.
Operator
Description
+
adds two operands
–
subtract second operands from first
*
multiply two operand
/
divide numerator by denominator
%
remainder of division
++
Increment operator – increases integer value by one
—
Decrement operator – decreases integer value by one
Relational operators:-
The following table shows all relation operators supported by C.
Operator
Description
==
Check if two operand are equal
!=
Check if two operand are not equal.
>
Check if operand on the left is greater than operand on the right
<
Check operand on the left is smaller than right operand
>=
check left operand is greater than or equal to right operand
<=
Check if operand on left is smaller than or equal to right operand
Logical operators:-
C language supports following 3 logical operators. Suppose a = 1 and b = 0,
Operator
Description
Example
&&
Logical AND
(a && b) is false
||
Logical OR
(a || b) is true
!
Logical NOT
(!a) is false
Bitwise operators:-
Bitwise operators perform manipulations of data at bit level. These operators also perform shifting of bits from right to left. Bitwise operators are not applied to float or double(These are datatypes, we will learn about them in the next tutorial).
Operator
Description
&
Bitwise AND
|
Bitwise OR
^
Bitwise exclusive OR
<<
left shift
>>
right shift
Assignment Operators:-
Assignment operators supported by C language are as follows.
Operator
Description
Example
=
assigns values from right side operands to left side operand
a=b
+=
adds right operand to the left operand and assign the result to left
a+=b is same as a=a+b
-=
subtracts right operand from the left operand and assign the result to left operand
a-=b is same as a=a-b
*=
mutiply left operand with the right operand and assign the result to left operand
a*=b is same as a=a*b
/=
divides left operand with the right operand and assign the result to left operand
a/=b is same as a=a/b
%=
calculate modulus using two operands and assign the result to left operand
a%=b is same as a=a%b
Conditional operator:-
The Conditional Operator in C, also called a Ternary operator, is one of the Operators, which used in the decision-making process. The C Programming Conditional Operator returns the statement depends upon the given expression result.
Each variable in C has an associated data type. Each data type requires different amounts of memory and has some specific operations which can be performed over it.Each variable in C has an associated data type. Each data type requires different amounts of memory and has some specific operations which can be performed over it.
Every C compiler supports five primary data types:
void
As the name suggests, it holds no value and is generally used for specifying the type of function or what it returns. If the function has a void type, it means that the function will not return any value.
int
Used to denote an integer type.
char
Used to denote a character type.
float, double
Used to denote a floating point type.
int *, float *, char *
Used to denote a pointer type.
Derived Data Types
C supports three derived data types:
Data Types
Description
Arrays
Arrays are sequences of data items having homogeneous values. They have adjacent memory locations to store values.
References
Function pointers allow referencing functions with a particular signature.
Pointers
These are powerful C features which are used to access the memory and deal with their addresses.
User defined data type
C allows the feature called type definition which allows programmers to define their identifier that would represent an existing data type. There are three such types:
Data Types
Description
Structure
It is a package of variables of different types under a single name. This is done to handle data efficiently. “struct” keyword is used to define a structure.
Union
These allow storing various data types in the same memory location. Programmers can define a union with different members, but only a single member can contain a value at a given time. It is used for
Enum
Enumeration is a special data type that consists of integral constants, and each of them is assigned with a specific name. “enum” keyword is used to define the enumerated data type.
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