Friday, 28 June 2013

Amazon Cloud Drive: An Efficient Online Cloud File Storage Software and Service

Amazon Cloud Drive: An Efficient Online Cloud File Storage Software and Service

Amazon Cloud Drive provides a lot of features and benefits which will make you to choose amazon cloud drive to store your important files, documents, photos, videos etc. on cloud. You can store and access your files with ease anywhere anytime securely. You will get 5GB of free file storage space when you install Amazon Cloud Drive for Windows and Mac. Following are some of the features of Amazon Cloud Drive discussed in detail.

Online Quick and Reliable File Storage

Never worry about losing a precious memory or not having access to your important files on the go. Amazon Cloud Drive makes storing your photos, videos, documents, and other digital files in the Cloud quick and easy. Get started with 5 GB of free storage--enough space to store up to 2,000 photos.

File Storage Security

Protecting your files in the Cloud is as easy as moving files to your Cloud Drive folder after installing the Cloud Drive app for Windows and Mac. You can also install Cloud Drive Photos for Android and iPhone to easily upload photos from your phone or tablet so you never have to worry about losing precious memories if your phone is lost or damaged. If you're on the go and need a file stored in Cloud Drive, you can quickly access it from any web browser.

Easy Access to Your Files

Your photos are always close at hand on your Kindle Fire, iPhone, or Android phone or tablet. Kindle Fire (latest-generation) and Kindle Fire HD put documents stored in Cloud Drive within easy reach and bring your photos to life in stunning fashion. Using your iPhone or Android phone or tablet you can also browse your photos on the go with Cloud Drive Photos.

Friday, 21 June 2013

Apple iCloud Features: A Cloud Storage Service Provided by Apple

Apple iCloud Features: A Cloud Storage Service Provided by Apple

If you want to store your documents, files, photos, videos, email, business services and operations online on the cloud, you should consider Apple iCloud. iCloud is the one of the best cloud online file storage service available in the cloud market. As this is the product of Apple, iCloud is equipped with a lot of exciting features and functionalities. Following is the list of features provided by iCloud like Mobile Access, Ease of Use, Technical Support etc. Lets discuss all these iCloud features in detail:

Mobile Access:

Naturally, access to iCloud primarily falls within the realms of the Apple ecosystem; the cloud service is compatible with the iPhone, iPad and iPod Touch, and will be with any future iOS device. You can also sync a Mac with iCloud, and in a most surprising compromise, a Windows-based PC as well. Additionally, you can access the web interface of your iCloud account from any web browser.

Still, iCloud remains at the bottom of the pack with its limited mobile access. You can’t log in via a mobile browser and the service is not compatible with competing mobile devices, such as Android and Blackberry.

Ease of Use:

When it comes to ease of use, iCloud easily outpaces the competition. It’s not so much that the other cloud services are difficult to use (they aren’t), it’s merely that iCloud has done it the simplest. All of your files are in one place and it doesn’t require any hands-on management; you simply download or save a file once and it is instantly available on all of your devices. The service is intuitive and easy to navigate, and even those timid about using cloud services will find this one accessible and remarkably uncomplicated. Furthermore, iCloud, like all of Apple’s products, is sleek, stylish and sophisticated.

Help & Support:

As one of the most well-known technology companies in the world, Apple continually scores high marks in customer satisfaction, providing comprehensive tech support for all of its products and services. iCloud is no exception, supplemented with useful online resources and direct technical support. If you want to learn more about the service, peruse the iCloud support center, where you’ll find answers to your questions about using iCloud. For troubleshooting assistance, you can contact Apple directly via toll-free telephone or email, or participate on threads in the iCloud customer communities.

Summary:

As expected, the cloud service works beautifully and seamlessly within the Apple ecosystem. It’s sleek, robust and extremely user-friendly. iCloud is a must if you are a consumer or small business already using Apple products; you’ll be able to access all your digital files and media anytime and from any one of your Apple devices without having to manually sync them.

Thursday, 20 June 2013

How to Choose Best Cloud Storage / Hosting Service Provider?

How to Choose Best Cloud Storage / Hosting Service Provider?

As the market demand for cloud hosting is increasing day by day. A lot of cloud hosting service providers have jumped into the cloud storage market who claim they are best in cloud hosting. Major cloud storage service providers are Amazon, Cisco, Citrix, Apple, Google, Microsoft, IBM, Rackspace, Salesforce and Verizon. So I think this is the time to compare the cloud hosting services provided by various cloud hosting providers. There are a lot of factors like security, reliability, storage space, cloud hosting cost, technical support to be considered before choosing a cloud storage service provider.

Factors to be considered before choosing any Cloud Storage / Hosting Service Providers

As we know Amazon, Cisco, Citrix, Apple, Google, Microsoft, IBM, Rackspace, Salesforce and Verizon are the big cloud storage and hosting service providers in the cloud market. Before choosing any cloud service providers you need to keep some points and features which you need in your cloud service provider. Lets discuss them first.

1. Cloud Storage Security

As you are going to host / store your critical business operations like emails, documents, business services etc on the cloud to reduce your software maintenance cost and streamline your business operations, you must think of security first. Is your critical data which is stored on the cloud secured? If yes, then think for other features, otherwise if you have doubts, don't go for that cloud storage service provider. Cloud providers should have several standard security measures in place and constantly update them.

Security measures to look for include firewalls, anti-virus detection, multifactor user authentication and data encryption, and routine security audits. It's also important to ask who at
the cloud company will have access to your data in the cloud and whether the cloud provider does employee background checks to weed out potential cybercriminals or identity thieves.

Cloud service providers also should answer questions about compliance with government legislation specific to your industry. For example, if your business is in the healthcare industry, you'll want to be sure your cloud provider is compliant with the Health Insurance Portability and Accountability Act (HIPAA), which deals with patient data privacy and security.

CSA (Cloud Security Alliance) is an organization which provides certificates to the cloud service providers if CSA feels that cloud service is secure. So must check for these kind of security certifications that your cloud service provider has.

The location and security of the data centers and servers where your company's information will be stored are as important as online security. You should ask how a potential cloud vendor protects its data center from natural disasters, including fires, floods, earthquakes and storms. Also, find out how the facilities are protected from thieves who could walk away with your sensitive data.

You must ask for SSAE 16 certification of cloud hosting provider. SSAE 16 certification demonstrates that a company's products, systems and data are compliant with the industry security standards for customer access and privacy, data center physical security and data redundancy.

On the off chance your cloud provider accidentally deletes or loses your precious data, you need to know how it will rectify the problem. Will the provider compensate you for losses? What data redundancies does it have in place to mitigate the risks of data loss? It's also important to ask if the company has experienced any significant issues resulting from the loss of customer data.

2. Cloud Storage Reliability

Reliability for cloud storage is another consideration. Your data, documents, emails, business services should always be available and accessible to you at any time. You must read SLA (Service Level Agreement) of the cloud service providers carefully and enquire about the service outages. Cloud service provider should compensate you in case the outage is longer than mentioned in SLA. So you should have this idea in your mind that how much outage is feasible for your business.

Because cloud outages can be disruptive and costly for your business, it's best to choose a provider with as few as possible. Some vendors post their downtime history logs online. If not, be sure to ask for a cloud provider's track record.

3. Cloud Storage Space

You must ensure how much storage space is provided by the cloud hosting service provider and is that much storage space is okay for your business needs. What if in future you need more space? What would be the extra cost for that space?

To ensure that you're choosing a flexible cloud provider, find out what additional storage capacity and other services can be offered over time and for how much. If you plan to increase your staff, you'll want to make sure that you can easily add additional users to your account.

4. Cloud Hosting Cost

After ensuring all above, consider cost of the cloud service. Is that cost comes into your budget or not. The cloud storage cost can be based on pre-user utility model but there can be many other factors and variations. The physical location of the servers may also be a factor for sensitive data. You should confirm the pricing structure beforehand. You should only pay for what you use. The pricing scheme should be pay-as-you go from the outset, with the ability to add services as needed. Fees can typically be charged hourly, monthly, semi-annually or annually, depending on the vendor.

5. Customer Support Service

Technical support should be available to you online or by phone 24 hours a day, every day, including holidays. You should also inquire about the average response and resolution time, and whether you'll be interacting with knowledgeable engineers or customer service reps reading scripts when you call the customer help line or use a live chat feature.

Saturday, 15 June 2013

Types of Bindings in WCF: Encoding Methods and Protocols

Types of Bindings in WCF: Encoding Methods and Protocols

Bindings in WCF define that how to communicate with the service. So, WCF Binding specifies that which communication protocol and encoding method should be used to communicate with the service.

WCF comes with a number of built-in bindings that we can use to expose our service, but WCF is extensible so we can define our own custom bindings to fulfill specific needs. WCF Binding can be BasisHttpBinding, WsHttpBinding, WsDualHttpBinding, WsFederationHttpBinding, NetNamedPipeBinding, NetTcpBinding, NetPeerTcpBinding, NetMsmqBinding. Lets look at them in detail:

Types of WCF Bindings

1. BasicHttpBinding is designed to replace ASMX Web services. It supports both HTTP and Secure HTTP. As far as encoding is concerned, it provides support for Text as well as MTOM encoding methods. BasicHttpBinding doesn’t support WS-* standards like WS-Addressing, WS-Security and WS-ReliableMessaging.

2. WsHttpBinding also supports interoperability. With this binding, the SOAP message is, by default, encrypted. It supports HTTP and HTTPS. In terms of encoding, it provides support for Text as well as MTOM encoding methods. It supports WS-* standards like WS-Addressing, WS-Security and WS-ReliableMessaging. By default, reliable sessions are disabled because it can cause a bit of performance overhead.

3. WsDualHttpBinding has all features of WsHttpBinding with addition that it supports Duplex MEP (Message Exchange Pattern). In this MEP, service can communicate with client via callback. Its basically a two way communication.

4. WsFederationHttpBinding is a specialized form of WS Binding that offers support for federated security.

5. NetNamedPipeBinding is secure and reliable binding on a single WCF computer across process communication. It provides support for binary encoding which is the best 

6. NetTcpBinding supports reliability, transactions and security. It also supports TCP protocol and binary as encoding method. We can say that it’s the most optimized or fastest binding because both client and service are on the same WCF technology.

7. NetPeerTcpBinding supports features as that of netTcpBinding but it provides secure binding for peer-to-peer environment with WCF Services.

8. NetMsmqBinding is required in a cross machine environment with secure and reliable queued communication. This uses MSMQ as transport.

Tuesday, 11 June 2013

Unix Basic Commands Interview Questions and Answers

Unix Basic Commands Interview Questions and Answers

Following is the list of unix basic commands interview questions and answers. These are very basic unix commands and you must know these commands if you are going to appear in a unix interview. I have listed down 31 unix interview questions with answers which cover basic unix commands like ls, banner, cat, date, tee, who, man, head, pg, cmp, diff, grep, kill, echo, su etc. So lets have a look on following unix interview questions and commands.

1. Construct pipes to execute the following jobs.

1. Output of who should be displayed on the screen with value of total number of users who have logged in displayed at the bottom of the list.

2. Output of ls should be displayed on the screen and from this output the lines containing the word ‘poem’ should be counted and the count should be stored in a file.

3. Contents of file1 and file2 should be displayed on the screen and this output should be appended in a file. From output of ls the lines containing ‘poem’ should be displayed on the screen along with the count.

4. Name of cities should be accepted from the keyboard . This list should be combined with the list present in a file. This combined list should be sorted and the sorted list should be stored in a file ‘newcity’.

5. All files present in a directory dir1 should be deleted any error while deleting should be stored in a file ‘errorlog’.

2. Explain the following commands.

$ ls > file1
$ banner hi-fi > message
$ cat par.3 par.4 par.5 >> report
$ cat file1>file1
$ date ; who
$ date ; who > logfile
$ (date ; who) > logfile

3. What is the significance of the “tee” command?

It reads the standard input and sends it to the standard output while redirecting a copy of what it has read to the file specified by the user.

4. What does the command “ $who | sort –logfile > newfile” do?

The input from a pipe can be combined with the input from a file . The trick is to use the special symbol “-“ (a hyphen) for those commands that recognize the hyphen as std input. In the above command the output from who becomes the std input to sort , meanwhile sort opens the file logfile, the contents of this file is sorted together with the output of who (rep by the hyphen) and the sorted output is redirected to the file newfile.

5. What does the command “$ls | wc –l > file1” do?

ls becomes the input to wc which counts the number of lines it receives as input and instead of displaying this count , the value is stored in file1.

6. Which of the following commands is not a filter man , (b) cat , (c) pg , (d) head

Ans: man
A filter is a program which can receive a flow of data from std input, process (or filter) it and send the result to the std output. 

7. How is the command “$cat file2 “ different from “$cat >file2 and >> redirection operators?

8. Explain the steps that a shell follows while processing a command.

After the command line is terminated by the key, the shell goes ahead with processing the command line in one or more passes. The sequence is well defined and assumes the following order.

Parsing: The shell first breaks up the command line into words, using spaces and the delimiters, unless quoted. All consecutive occurrences of a space or tab are replaced here with a single space.

Variable evaluation: All words preceded by a $ are avaluated as variables, unless quoted or escaped. 

Command substitution: Any command surrounded by backquotes is executed by the shell which then replaces the standard output of the command into the command line.

Wild-card interpretation: The shell finally scans the command line for wild-cards (the characters *, ?, [, ]). Any word containing a wild-card is replaced by a sorted list of filenames that match the pattern. The list of these filenames then forms the arguments to the command.

PATH evaluation: It finally looks for the PATH variable to determine the sequence of directories it has to search in order to hunt for the command.

9. What difference between cmp and diff commands?

cmp - Compares two files byte by byte and displays the first mismatch
diff - tells the changes to be made to make the files identical

11. What is the use of ‘grep’ command?

‘grep’ is a pattern search command. It searches for the pattern, specified in the command line with appropriate option, in a file(s).
Syntax : grep
Example : grep 99mx mcafile

12. What is the difference between cat and more command?

Cat displays file contents. If the file is large the contents scroll off the screen before we view it. So command 'more' is like a pager which displays the contents page by page.

13. Write a command to kill the last background job?

Kill $!

14. Which command is used to delete all files in the current directory and all its sub-directories?

rm -r *

15. Write a command to display a file’s contents in various formats?

$od -cbd file_name
c - character, b - binary (octal), d-decimal, od=Octal Dump.

16. What will the following command do?

$ echo *
It is similar to 'ls' command and displays all the files in the current directory.

17. Is it possible to create new a file system in UNIX?

Yes, ‘mkfs’ is used to create a new file system.

18. Is it possible to restrict incoming message?

Yes, using the ‘mesg’ command.

19. What is the use of the command "ls -x chapter[1-5]"

ls stands for list; so it displays the list of the files that starts with 'chapter' with suffix '1' to '5', chapter1, chapter2, and so on.

20. Is ‘du’ a command? If so, what is its use?

Yes, it stands for ‘disk usage’. With the help of this command you can find the disk capacity and free space of the disk.

21. Is it possible to count number char, line in a file; if so, How?

Yes, wc-stands for word count.
wc -c for counting number of characters in a file.
wc -l for counting lines in a file.

22. Name the data structure used to maintain file identification?

‘inode’, each file has a separate inode and a unique inode number.

23. How many prompts are available in a UNIX system?

Two prompts, PS1 (Primary Prompt), PS2 (Secondary Prompt).

24. How does the kernel differentiate device files and ordinary files?

Kernel checks 'type' field in the file's inode structure.

25. How to switch to a super user status to gain privileges?

Use ‘su’ command. The system asks for password and when valid entry is made the user gains super user (admin) privileges.

26. What are shell variables?

Shell variables are special variables, a name-value pair created and maintained by the shell.
Example: PATH, HOME, MAIL and TERM

27. What is redirection?

Directing the flow of data to the file or from the file for input or output.
Example : ls > wc

28. How to terminate a process which is running and the specialty on command kill 0?

With the help of kill command we can terminate the process.
Syntax: kill pid
Kill 0 - kills all processes in your system except the login shell.

29. What is a pipe and give an example?

A pipe is two or more commands separated by pipe char '|'. That tells the shell to arrange for the output of the preceding command to be passed as input to the following command.

Example : ls -l | pr

The output for a command ls is the standard input of pr.
When a sequence of commands are combined using pipe, then it is called pipeline.

30. Explain kill() and its possible return values.

There are four possible results from this call:

‘kill()’ returns 0. This implies that a process exists with the given PID, and the system would allow you to send signals to it. It is system-dependent whether the process could be a zombie.

‘kill()’ returns -1, ‘errno == ESRCH’ either no process exists with the given PID, or security enhancements are causing the system to deny its existence. (On some systems, the process could be a zombie.)

‘kill()’ returns -1, ‘errno == EPERM’ the system would not allow you to kill the specified process. This means that either the process exists (again, it could be a zombie) or draconian security enhancements are present

(e.g. your process is not allowed to send signals to *anybody*).

‘kill()’ returns -1, with some other value of ‘errno’ you are in trouble! The most-used technique is to assume that success or failure with ‘EPERM’ implies that the process exists, and any other error implies that it
doesn't.

An alternative exists, if you are writing specifically for a system (or all those systems) that provide a ‘/proc’ filesystem: checking for the existence of ‘/proc/PID’ may work.

31. What is relative path and absolute path.

Absolute path : Exact path from root directory.
Relative path : Relative to the current path.

Wednesday, 5 June 2013

C Advanced Interview Questions and Answers For Experienced Developers

C Advanced Interview Questions and Answers For Experienced Developers

I have compiled a list of advanced C interview questions and answers for experienced developers. There are 49 C interview questions and answers in this list. If you are going for C/C++ interview, you must read following list of C interview questions and answers. I have covered the various C concepts in these interview questions like memory allocation and deallocation using malloc and calloc, difference between printof and sprintof, linked lists, static variables and functions, storage classes, hashing, pointers, arguments, text and binary modes, linker, difference between switch and if and OOPS concepts like polymorphism, function and operator overloading etc. Lets have a look at following list of C advanced interview questions and answers: 

1. What is C language?

The C programming language is a standardized programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the UNIX operating system. 

It has since spread to many other operating systems, and is one of the most widely used programming languages. C is prized for its efficiency, and is the most popular programming language for writing system software, though it is also used for writing applications.

2. What is the output of printf("%d")?

A. When we write printf("%d",x); this means compiler will print the value of x. But as here, there is nothing after %d so compiler will show in output window garbage value.

B. When we use %d the compiler internally uses it to access the argument in the stack (argument stack). Ideally compiler determines the offset of the data variable depending on 

the format specification string. Now when we write printf("%d",a) then compiler first accesses the top most element in the argument stack of the printf which is %d and depending on the format string it calculated to offset to the actual data variable in the memory which is to be printed. Now when only %d will be present in the printf then compiler will calculate the correct offset (which will be the offset to access the integer variable) but as the actual data object is to be printed is not present at that memory location so it will print what ever will be the contents of that memory location.

C. Some compilers check the format string and will generate an error without the proper number and type of arguments for things like printf(...) and scanf(...).

3. What is the difference between "calloc(...)" and "malloc(...)"?

1. calloc(...) allocates a block of memory for an array of elements of a certain size. By default the block is initialized to 0. The total number of memory allocated will be (number_of_elements * size).

malloc(...) takes in only a single argument which is the memory required in bytes. malloc(...) allocated bytes of memory and not blocks of memory like calloc(...).

2. malloc(...) allocates memory blocks and returns a void pointer to the allocated space, or NULL if there is insufficient memory available.

calloc(...) allocates an array in memory with elements initialized to 0 and returns a pointer to the allocated space. calloc(...) calls malloc(...) in order to use the C++ set_new_mode function to set the new handler mode.

4. What is the difference between "printf(...)" and "sprintf(...)"?

sprintf(...) writes data to the character array whereas printf(...) writes data to the standard output device.

5. How to reduce a final size of executable?

Size of the final executable can be reduced using dynamic linking for libraries.

6. Can you tell me how to check whether a linked list is circular?

Create two pointers, and set both to the start of the list. Update each as follows:

while (pointer1) {
pointer1 = pointer1->next;
pointer2 = pointer2->next;
if (pointer2) pointer2=pointer2->next;
if (pointer1 == pointer2) {
print ("circular");
}}

If a list is circular, at some point pointer2 will wrap around and be either at the item just before pointer1, or the item before that. Either way, its either 1 or 2 jumps until they meet.

7. What is the output of the following program? Why?

#include
main() {
typedef union {
int a;
char b[10];
float c;
}
Union;
Union x,y = {100};
x.a = 50;
strcpy(x.b,"hello");
x.c = 21.50;
printf("Union x : %d %s %f n",x.a,x.b,x.c);
printf("Union y : %d %s %f n",y.a,y.b,y.c);
}

8. What does static variable mean?

There are 3 main uses for the static.

1. If you declare within a function:
It retains the value between function calls

2.If it is declared for a function name:
By default function is extern..so it will be visible from other files if the function declaration is as static..it is invisible for the outer files

3. Static for global variables:
By default we can use the global variables from outside files If it is static global..that variable is limited to with in the file 

9. What are the advantages of a macro over a function?

Macro gets to see the Compilation environment, so it can expand __ __TIME__ __FILE__ #defines. It is expanded by the preprocessor.

For example, you can’t do this without macros
#define PRINT(EXPR) printf( #EXPR “=%d\n”, EXPR)

PRINT( 5+6*7 ) // expands into printf(”5+6*7=%d”, 5+6*7 );

You can define your mini language with macros:
#define strequal(A,B) (!strcmp(A,B))

Macros are a necessary evils of life. The purists don’t like them, but without it no real work gets done.

10. What are the differences between malloc() and calloc()?

There are 2 differences.

First, is in the number of arguments. malloc() takes a single argument(memory required in bytes), while calloc() needs 2 arguments(number of variables to allocate memory, size in bytes of a single variable).

Secondly, malloc() does not initialize the memory allocated, while calloc() initializes the allocated memory to ZERO.

11. What are the different storage classes in C?

C has three types of storage: automatic, static and allocated. Variable having block scope and without static specifier have automatic storage duration.

Variables with block scope, and with static specifier have static scope.

Global variables (i.e, file scope) with or without the static specifier also have static scope.

Memory obtained from calls to malloc(), alloc() or realloc() belongs to allocated storage class.

12. What is the difference between strings and character arrays?

A major difference is: string will have static storage duration, whereas as a character array will not, unless it is explicity specified by using the static keyword. Actually, a string is a character array with following properties:

* the multibyte character sequence, to which we generally call string, is used to initialize an array of static storage duration. The size of this array is just sufficient to contain these characters plus the terminating NULL character.

* it not specified what happens if this array, i.e., string, is modified.

* Two strings of same value[1] may share same memory area. For example, in the following declarations:

char *s1 = “Calvin and Hobbes”;
char *s2 = “Calvin and Hobbes”;

The strings pointed by s1 and s2 may reside in the same memory location. But, it is not true for the following:

char ca1[] = “Calvin and Hobbes”;
char ca2[] = “Calvin and Hobbes”;

[1] The value of a string is the sequence of the values of the contained characters, in order.

13. What is the difference between const char* p and char const* p?

In const char* p, the character pointed by ‘p’ is constant, so u cant change the value of character pointed by p but u can make ‘p’ refer to some other location.

In char const* p, the ptr ‘p’ is constant not the character referenced by it, so u cant make ‘p’ to reference to any other location but u can change the value of the char pointed by ‘p’.

14. What is hashing?

To hash means to grind up, and that’s essentially what hashing is all about. The heart of a hashing algorithm is a hash function that takes your nice, neat data and grinds it into some random-looking integer.

The idea behind hashing is that some data either has no inherent ordering (such as images) or is expensive to compare (such as images). If the data has no inherent ordering, you can’t perform comparison searches.

If the data is expensive to compare, the number of comparisons used even by a binary search might be too many. So instead of looking at the data themselves, you’ll condense 

(hash) the data to an integer (its hash value) and keep all the data with the same hash value in the same place. This task is carried out by using the hash value as an index into an array.

To search for an item, you simply hash it and look at all the data whose hash values match that of the data you’re looking for. This technique greatly lessens the number of items you have to look at. If the parameters are set up with care and enough storage is available for the hash table, the number of comparisons needed to find an item can be made arbitrarily close to one.

One aspect that affects the efficiency of a hashing implementation is the hash function itself. It should ideally distribute data randomly throughout the entire hash table, to reduce the likelihood of collisions. Collisions occur when two different keys have the same hash value. 

There are two ways to resolve this problem. In open addressing, the collision is resolved by the choosing of another position in the hash table for the element inserted later. When the hash table is searched, if the entry is not found at its hashed position in the table, the search continues checking until either the element is found or an empty position in the table is found.

The second method of resolving a hash collision is called chaining. In this method, a bucket or linked list holds all the elements whose keys hash to the same value. When the hash table is searched, the list must be searched linearly.

15. How can you determine the size of an allocated portion of memory?

You can’t, really. free() can , but there’s no way for your program to know the trick free() uses. Even if you disassemble the library and discover the trick, there’s no guarantee the trick won’t change with the next release of the compiler.

16. Can static variables be declared in a header file?

You can’t declare a static variable without defining it as well (this is because the storage class modifiers static and extern are mutually exclusive). A static variable can be defined in a header file, but this would cause each source file that included the header file to have its own private copy of the variable, which is probably not what was intended.

17. Can a variable be both const and volatile?

Yes. The const modifier means that this code cannot change the value of the variable, but that does not mean that the value cannot be changed by means outside this code.

18. Can include files be nested?

Yes. Include files can be nested any number of times. As long as you use precautionary measures , you can avoid including the same file twice. In the past, nesting header files was seen as bad programming practice, because it complicates the dependency tracking function of the MAKE program and thus slows down compilation. Many of today’s popular compilers make up for this difficulty by implementing a concept called precompiled headers, in which all headers and associated dependencies are stored in a precompiled state.

Many programmers like to create a custom header file that has #include statements for every header needed for each module. This is perfectly acceptable and can help avoid potential problems relating to #include files, such as accidentally omitting an #include file in a module.

19. When does the compiler not implicitly generate the address of the first element of an array?

Whenever an array name appears in an expression such as

- array as an operand of the sizeof operator
- array as an operand of & operator
- array as a string literal initializer for a character array

Then the compiler does not implicitly generate the address of the address of the first element of an array.

20. What is a null pointer?

There are times when it’s necessary to have a pointer that doesn’t point to anything. The macro NULL, defined in , has a value that’s guaranteed to be different from any valid pointer. NULL is a literal zero, possibly cast to void* or char*. Some people, notably C++ programmers, prefer to use 0 rather than NULL.

The null pointer is used in three ways:

1) To stop indirection in a recursive data structure
2) As an error value
3) As a sentinel value

21. What is the difference between text and binary modes?

Streams can be classified into two types: text streams and binary streams. Text streams are interpreted, with a maximum length of 255 characters. With text streams, carriage return/line feed combinations are translated to the newline n character and vice versa. Binary streams are uninterrupted and are treated one byte at a time with no translation of characters. Typically, a text stream would be used for reading and writing standard text files, printing output to the screen or printer, or receiving input from the keyboard.

A binary text stream would typically be used for reading and writing binary files such as graphics or word processing documents, reading mouse input, or reading and writing to the modem.

22. What is static memory allocation and dynamic memory allocation?

Static memory allocation: The compiler allocates the required memory space for a declared variable.By using the address of operator,the reserved address is obtained and this address may be assigned to a pointer variable.Since most of the declared variable have static memory,this way of assigning pointer value to a pointer variable is known as static memory allocation. memory is assigned during compilation time.

Dynamic memory allocation: It uses functions such as malloc( ) or calloc( ) to get memory dynamically.If these functions are used to get memory dynamically and the values returned by these functions are assingned to pointer variables, such assignments are known as dynamic memory allocation.memory is assined during run time.

23. When should a far pointer be used?

Sometimes you can get away with using a small memory model in most of a given program. There might be just a few things that don’t fit in your small data and code segments. 

When that happens, you can use explicit far pointers and function declarations to get at the rest of memory. A far function can be outside the 64KB segment most functions are shoehorned into for a small-code model. (Often, libraries are declared explicitly far, so they’ll work no matter what code model the program uses.) A far pointer can refer to information outside the 64KB data segment. Typically, such pointers are used with farmalloc() and such, to manage a heap separate from where all the rest of the data lives. If you use a small-data, large-code model, you should explicitly make your function pointers far.

24. How are pointer variables initialized?

Pointer variable are initialized by one of the following two ways

- Static memory allocation
- Dynamic memory allocation

25. What is the difference between arrays and pointers?

- Pointers are used to manipulate data using the address. Pointers use * operator to access the data pointed to by them

- Arrays use subscripted variables to access and manipulate data. Array variables can be equivalently written using pointer expression.

26. Is using exit() the same as using return?

No. The exit() function is used to exit your program and return control to the operating system. The return statement is used to return from a function and return control to the calling function. If you issue a return from the main() function, you are essentially returning control to the calling function, which is the operating system. In this case, the return statement and exit() function are similar.

27. What is a method?

Method is a way of doing something, especially a systematic way; implies an orderly logical arrangement (usually in steps). 

28. What is indirection?

If you declare a variable, its name is a direct reference to its value. If you have a pointer to a variable, or any other object in memory, you have an indirect reference to its value.

29. What is modular programming?

If a program is large, it is subdivided into a number of smaller programs that are called modules or subprograms. If a complex problem is solved using more modules, this approach is known as modular programming.

30. How many levels deep can include files be nested?

Even though there is no limit to the number of levels of nested include files you can have, your compiler might run out of stack space while trying to include an inordinately high number of files. This number varies according to your hardware configuration and possibly your compiler.

31. What is the difference between declaring a variable and defining a variable?

Declaring a variable means describing its type to the compiler but not allocating any space for it. Defining a variable means declaring it and also allocating space to hold the variable. You can also initialize a variable at the time it is defined.

32. What is an lvalue?

An lvalue is an expression to which a value can be assigned. The lvalue expression is located on the left side of an assignment statement, whereas an rvalue is located on the right side of an assignment statement. Each assignment statement must have an lvalue and an rvalue. The lvalue expression must reference a storable variable in memory. It cannot be a constant.

33. Differentiate between an internal static and external static variable?

An internal static variable is declared inside a block with static storage class whereas an external static variable is declared outside all the blocks in a file.An internal static variable has persistent storage, block scope and no linkage.An external static variable has permanent storage,file scope and internal linkage.

34. What is the difference between a string and an array?

An array is an array of anything. A string is a specific kind of an array with a well-known convention to determine its length. There are two kinds of programming languages: those in which a string is just an array of characters, and those in which it’s a special type. In C, a string is just an array of characters (type char), with one wrinkle: a C string always ends with a NUL character.

The “value” of an array is the same as the address of (or a pointer to) the first element; so, frequently, a C string and a pointer to char are used to mean the same thing.

An array can be any length. If it’s passed to a function, there’s no way the function can tell how long the array is supposed to be, unless some convention is used. The convention for strings is NULL termination; the last character is an ASCII NULL (‘’) character.

35. What is an argument? Differentiate between formal arguments and actual arguments?

An argument is an entity used to pass the data from calling function to the called function. Formal arguments are the arguments available in the function definition. They are preceded by their own data types. Actual arguments are available in the function call.

36. What are advantages and disadvantages of external storage class?

Advantages of external storage class

1)Persistent storage of a variable retains the latest value
2)The value is globally available

Disadvantages of external storage class

1)The storage for an external variable exists even when the variable is not needed
2)The side effect may produce surprising output
3)Modification of the program is difficult
4)Generality of a program is affected

37. What is a void pointer?

A void pointer is a C convention for a raw address. The compiler has no idea what type of object a void Pointer really points to. If you write int *ip; ip points to an int. If you write void *p; p doesn’t point to a void! 

In C and C++, any time you need a void pointer, you can use another pointer type. For example, if you have a char*, you can pass it to a function that expects a void*. You don’t even need to cast it. In C (but not in C++), you can use a void* any time you need any kind of pointer, without casting. (In C++, you need to cast it). 

A void pointer is used for working with raw memory or for passing a pointer to an unspecified type. Some C code operates on raw memory. When C was first invented, character pointers (char *) were used for that. Then people started getting confused about when a character pointer was a string, when it was a character array, and when it was raw memory.

38. When should a type cast not be used?

A type cast should not be used to override a const or volatile declaration. Overriding these type modifiers can cause the program to fail to run correctly. A type cast should not be used to turn a pointer to one type of structure or data type into another. In the rare events in which this action is beneficial, using a union to hold the values makes the programmer’s intentions clearer.

39. When is a switch statement better than multiple if statements?

A switch statement is generally best to use when you have more than two conditional expressions based on a single variable of numeric type.

40. What is a static function?

A static function is a function whose scope is limited to the current source file. Scope refers to the visibility of a function or variable. If the function or variable is visible outside of the current source file, it is said to have global, or external, scope. If the function or variable is not visible outside of the current source file, it is said to have local, or static, scope.

41. What is a pointer variable?

A pointer variable is a variable that may contain the address of another variable or any valid address in the memory.

42. What is a pointer value and address?

A pointer value is a data object that refers to a memory location. Each memory location is numbered in the memory. The number attached to a memory location is called the address of the location.

43. What is a modulus operator? What are the restrictions of a modulus operator?

A Modulus operator gives the remainder value. The result of x%y is obtained by (x-(x/y)*y). This operator is applied only to integral operands and cannot be applied to float or double.

44. Differentiate between a linker and linkage?

A linker converts an object code into an executable code by linking together the necessary build in functions. The form and place of declaration where the variable is declared in a program determine the linkage of variable.

45. What is a function and built-in function?

A large program is subdivided into a number of smaller programs or subprograms. Each subprogram specifies one or more actions to be performed for a large program. such subprograms are functions. The function supports only static and extern storage classes. By default, function assumes extern storage class. functions have global scope. Only register or auto storage class is allowed in the function parameters. Built-in functions that predefined and supplied along with the compiler are known as built-in functions. They are also known as library functions.

46. Why should I prototype a function?

A function prototype tells the compiler what kind of arguments a function is looking to receive and what kind of return value a function is going to give back. This approach helps the compiler ensure that calls to a function are made correctly and that no erroneous type conversions are taking place.

47. What is Polymorphism?

'Polymorphism' is an object oriented term. Polymorphism may be defined as the ability of related objects to respond to the same message with different, but appropriate actions. In other words, polymorphism means taking more than one form. Polymorphism leads to two important aspects in Object Oriented terminology - Function Overloading and Function Overriding. Overloading is the practice of supplying more than one definition for a given function name in the same scope. The compiler is left to pick the appropriate version of the function or operator based on the arguments with which it is called.

Overriding refers to the modifications made in the sub class to the inherited methods from the base class to change their behavior. 

48. What is Operator overloading?

When an operator is overloaded, it takes on an additional meaning relative to a certain class. But it can still retain all of its old meanings. 

Examples:

1) The operators >> and << may be used for I/O operations because in the header, they are overloaded.

2) In a stack class it is possible to overload the + operator so that it appends the contents of one stack to the contents of another. But the + operator still retains its original meaning relative to other types of data.

49. What is the difference between goto and longjmp() and setjmp()?

A goto statement implements a local jump of program execution, and the longjmp() and setjmp() functions implement a nonlocal, or far, jump of program execution.

Generally, a jump in execution of any kind should be avoided because it is not considered good programming practice to use such statements as goto and longjmp in your program. 

A goto statement simply bypasses code in your program and jumps to a predefined position. To use the goto statement, you give it a labeled position to jump to. This predefined position must be within the same function. You cannot implement gotos between functions.

When your program calls setjmp(), the current state of your program is saved in a structure of type jmp_buf. Later, your program can call the longjmp() function to restore the program’s state as it was when you called setjmp().Unlike the goto statement, the longjmp() and setjmp() functions do not need to be implemented in the same function.

However, there is a major drawback to using these functions: your program, when restored to its previously saved state, will lose its references to any dynamically allocated memory between the longjmp() and the setjmp(). This means you will waste memory for every malloc() or calloc() you have implemented between your longjmp() and setjmp(), and your program will be horribly inefficient.

It is highly recommended that you avoid using functions such as longjmp() and setjmp() because they, like the goto statement, are quite often an indication of poor programming practice.