Fibonacci series by Recursion in c

Introduction:-

Recursion is the process of repeating items in a self-similar way. In other words recursion is a process in which a same set of a statement/expressions are executed large no of times in such a manner that after the execution of a certain set of a statement/expression, again the same set of a statement/expressions are being executed until the condition is satisfied. Generally this kind of a process takes place in the in functions in which a function calls itself. The following is the syntax of the recursive function:-

void recursion()
{
   recursion(); /* function calls itself */
}

int main()
{
   recursion();
}

Actually most of the programming languages support recursion an C programming language is one of them i.e., a function to call itself. But while using recursion, programmers need to be careful to define an exit condition from the function, otherwise it will go in infinite loop.

Recursive function are very useful to solve many mathematical problems like to calculate factorial of a number, generating Fibonacci series, etc.

Program me:-

/* Fibonacci by Recursion */




#include<stdio.h>


int fib(int);

int main()
{
 printf("Type any value : ");
 printf("\nNth value: %d",fib(getche()-'0'));
 return 0;
}

int fib(int n)
{
 if(n<=1)
  return n;
 return(fib(n-1)+fib(n-2));
}

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C Programming to Explain Type Casting

Introduction:-

Type casting is a way to convert a variable from one data type to another data type. For example, if you want to store a long value into a simple integer then you can type cast long to int. You can convert values from one type to another explicitly using the cast operator as follows:

Program me:-

#include< stdio.h>
#include< conio.h>
int main( )
{
int n,i,j,fact;
float sum=0;
clrscr();
for(i=1; i<=7; i++) { fact=1; for(j=i; j>=1; j--)                       // to find the factorial
fact=fact*j;

sum=sum+(float)i/fact;
}
printf("\nSum : %f",sum);
getch();
return 0;
}

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Modifiers in C Programming Language

As We Have discussed in the last article about C Programming   the data types have some modifiers preceding them. The use of these modifiers changes the meaning of the base type.

The memory in the computer is organized in terms of units called bytes. One  byte consists of 8 bits and bit is a smallest unit of memory.

Need of Data Modifiers:

The Need of modifiers can be understood by the help of following.Let us take an example of a Program where we need to input the “Salary” of “Employees” in a team. This program will accept the salary as an input from user and then calculate the Income Tax of that user. We use “int” to store the Salary of the employee as we are assuming that the salary will be in “Whole Numbers”.

An integer data type takes 2 Bytes of Memory and we are aware that the Salary of any of the employee can not be “Negative”. We are using “2 Bytes” to store the memory of an Employee and we can easily save 1 Byte over there by removing the “Signed Part” in the integer. This positive value can easily be stored in “1 Bye Int” This leads us to the user of Data Type Modifiers.

Types of Data Modifiers in C:

Basically c programming language consist of 3 basic modifiers.The modifiers are listed below :

Signed Type Modifier:

All data types are “signed” by default. Signed Data Modifier implies that the data type variable can store positive values as well as negative values.

For example, if we need to declare a variable to store temperature, it can be negative as well as positive.

signed int temperature;

Or

int temperature;

Unsigned Type Modifier:

If we need to change the data type so that it can only store only store positive values, “unsigned” data modifier is used.

For example, if we need to declare a variable to store the salary of an employee as explained above, we will use “Unsigned” Data Qualifier here.

unsigned int salary;

Long Type Modifier:

Sometimes while coding a program, we need to increase the Storage Capacity of a variable so that it can store values higher than its maximum limit which is there as default. In such situations or programs, we need to make use of the “long” data type qualifier. “long” type modifier doubles the “length” of the data type when used along with it.

For example, if we need to store the “annual turnover” of a company in a variable, we will make us of this type qualifier.

long int turnover;

This variable will take 4 Bytes in memory.

Short Type Modifier:

A “short” type modifier does just the opposite of “long”. If one is not expecting to see high range values in a program and the values are both positive & negative.

For example, if we need to store the “age” of a student in a variable, we will make use of this type qualifier as we are aware that this value is not going to be very high.

short int age;

This variable will consume only 1 Byte in memory.

Example

We can apply the above mentioned modifiers to integer (int) and character (char) base types.

1. Integer Type Modifiers:

* We can use all the above mentioned Type Modifiers for int data type in C Language
* Short int and long int are also termed as short and long respectively.
* Int is signed & unsigned by default.

2. Character Type Modifiers:

* Variables of type char consume 1 byte in memory.
* Char can be signed or unsigned only.
* They have a range of -128 to 127 and 0 to 255 for signed & unsigned respectively.

3. Float Type & Double Type Modifier:

There are 3 types of float type modifiers as given below:

* float
* double
* long double

Double is same as long float. Float type occupies 4 bytes of memory. Type double occupies 8 bytes. Long double occupies 10 bytes. The exception to this is long double, which modifies the size of the double data type to 10 bytes. Please note that in some compilers this has no effect.


Note: We may use long modifier with double data type but it cannot be used with float, i.e. long double is allowed but long float is not allowed because long float is equal to double.

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C Programming Data Type

In C, variable(data) should be declared before it can be used in program. Data types are the keywords, which are used for assigning a type to a variable.In other words we can define the data type as a keyword which specifies the type of the data to be processed during the execution of the program me. 

Data types determine the following:

• Range of the data
• Type of the data stored
• Number of bytes it occupies in memory

C supports following data types:

• int – occupies 2 (16-bit compiler) or 4 bytes (32-bit compiler) of memory
• float – occupies 4 byes of memory
• double – occupies 8 bytes of memory
• char – occupies 1 byte of memory

Integer Data Type:-

int is used to define integer numbers. It occupies 2 bytes of memory (16-bit compiler).Keyword int is used for declaring the variable with integer type. For example:

1 2 3 4

{                                 int cost;                                 cost = 5;                 }

The size of int is either 2 bytes(In older PC's) or 4 bytes. If you consider an integer having size of 4 byte( equal to 32 bits), it can take 2³² distinct states as: -2³¹,-2³¹+1, ...,-2, -1, 0, 1, 2, ..., 2³¹-2, 2³¹-1

Similarly, int of 2 bytes, it can take 2¹⁶ distinct states from -2¹⁵ to 2¹⁵-1. If you try to store larger number than 2³¹-1, i.e,+2147483647 and smaller number than -2³¹, i.e, -2147483648,  program will not run correctly.

Float Data Type:-

float is used to define floating type numbers. It occupies 4 bytes of memory

(16-bit compiler).Variables of floating types can hold real values(numbers) such as: 2.34, -9.382 etc. Keywords either float or double is used for declaring floating type variable. For example:

1 2 3 4

{                                 float cost;                                 cost = 1.200000;                 }

Double Data Type:-

double is used to store big floating point numbers. It reserves 8 bytes of memory (16-bit compiler)

1 2 3 4

{                                 double cost;                                 cost = 1.200000000000;                 }

Difference between float and double:-

Generally the size of float(Single precision float data type) is 4 bytes and that of double(Double precision float data type) is 8 bytes. Floating point variables has a precision of 6 digits whereas the the precision of double is 14 digits.

Note: Precision describes the number of significant decimal places that a floating values carries.

Char Data Type:-

char is used to store characters. It occupies 1 byte of memory (16-bit compiler).The size of char is 1 byte. The character data type consists of ASCII characters. Each character is given a specific value. For example:

1 2 3 4

{                                 char alp;                                 alp = ‘A’;                 }

Summary:

Following table is applicable for 16-bit compiler.

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Literals in C Programming

The term literal constant or literal refers to a value that occurs in a program and cannot be changed. The C language uses the term constant in place of the noun literal. The adjective literal adds to the concept of a constant the notion that we can speak of it only in terms of its value. A literal constant is nonaddressable, which means that its value is stored somewhere in memory, but we have no means of accessing that address.

Every literal has a value and a data type. The value of any literal does not change while the program runs and must be in the range of representable values for its type. The following are the available types of literals:

Types:-

• Boolean
  
• Integer
• Character
• Floating-point
• String
• C Compound literal
• Vector literal

According to Wikipedia  a literal is a notation for representing a fixed value in source code. Almost all programming languages have notations for atomic values such as integers,floating-point numbers, and strings, and usually for booleans and characters; some also have notations for elements of enumerated types and compound values such as arrays,records, and objects. An anonymous function is a literal for the function type.

In contrast to literals, variables or constants are symbols that can take on one of a class of fixed values, the constant being constrained not to change. Literals are often used to initialize variables, for example, in the following, 1 is an integer literal and the three letter string in "cat" is a string literal:

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Constants, Variables and Keywords in C

Constants:-

A constant is an entity whose value does not change throughout the program execution.

There are rules to be followed in order to create a constant. Let us discuss the rules to create constants.

Rules for constructing Integer constant

1) An integer constant must have at least one digit.
2) It must not have a decimal point.
3) It can either be positive or negative.
4) No commas or blanks are allowed within an integer constant.

5) If no sign precedes an integer constant, it is assumed to be positive.
6) The allowable range for integer constants is -32768 to 32767


 Actually, the range of the integer constant depends on the compiler. The above mentioned range is for 16-bit compiler. However, for a 32-bit compiler the range would be even greater.

The integer constants
• Whole Numbers
• E.g. 50, 45, -35, -26
• Computer allocates only 2 bytes in memory.
• 16th bit is sign bit. (if 0 then positive value, if 1 then negative value)

Decimal Integer constant:
• 0 to 9
• E.g.: 49, 58, -62 … (40000 cannot come because it is > 32767)

Octal Integer constant:
• 0 to 7
• Add “0” before the value.
• E.g.: 045, 056, 067

Hexadecimal Integer constant:
• 0 to 9 and A to F
• Add 0x before the value
• E.g.: 0×42, 0×56, 0×67

Rules for constructing Real constants

Rules for constructing Real constants (Fractional Form)
1) A real constant must have at least one digit
2) It must have a decimal point
3) It could be either positive or negative
4) If no sign precedes an integer constant, it is assumed to be positive.
5) No commas or blanks are allowed within a real constant.

E.g.: +867.9, -26.9876, 654.0

Rules for constructing Real constants (Exponential Form)

1) The mantissa part and the exponential part should be separated by the letter ‘e’
2) The mantissa may have a positive or negative sign(default sign is positive)
3) The exponent must have at least one digit
4) The exponent must be a positive or negative integer(default sign is positive)
5) The range of real constants in exponential form is -3.4e38 and +3.4e38

E.g.: +3.2e-4, 4.1e8, -0.2e+4, -3.2e-4

Rules for constructing Character constant

1) A character constant is an alphabet, a single digit or a single special symbol enclosed within inverted commas. Both the inverted commas should point to the left. For example, ’S’ is a valid character constant whereas ‘S’ is not.
2) The maximum length of a character constant can be 1 character. Allots 1 byte of memory

Variable:-

A variable is an entity whose value keeps on changing throughout the program execution. However, it’s not a rule that the value of the variable will change. A variable value might remain same throughout the program execution. However the main difference between variable and constant is that we can’t change the value of constant in between the program, but we can change the value of the variable during program execution.

Rules for constructing variable names

A Variable name consists of any combination of alphabets, digits and underscores. Some compiler allows variable names whole length could be up to 247 characters. Still it would be safer to stick to the rule of 31 characters. Please avoid creating long variable name as it adds to your typing effort
The first character of the variable name must either be alphabet or underscore. It should not start with the digit
No commas and blanks are allowed in the variable name
No special symbols other than underscore are allowed in the variable name
We need to declare the type of the variable name before making use of that name in the program. Type declaration can be done as follows:

To declare a variable as integer, follow the below syntax:

int variable_name;
Here int is the type of the variable named variable_name. ‘int’ denotes integer type.

Following are the examples of type declaration statements:




E.g.:

int p, n;
float r;

keyword:-

Keywords are the words whose meaning has already been explained to the C compiler. The keyword cannot be used as the variable name. If we try to do so we are trying to assign new meaning to the keyword. The keywords are also known as ‘Reserved words’.

E.g.: for, if, static, while, do, break etc.

Let us take an example:-
We define a variable named x in a program. Let us say x=9.
After some time during execution we change the value of x to 10. Now, x=10.
Here value of x is getting changed. But the value of 9 and 10 will never change. Hence, x is called a variable and 9 is called a constant.

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What really happens when you navigate to a URL

1. You enter a URL into the browser 

 2. The browser looks up the IP address for the domain name 

Now the question comes in your mind What is DNS??????????

Answer is->Full Form of DNS is Domain Name System.The DNS translates Internet domain and host names to IP addresses. DNS automatically converts the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites.

The DNS lookup proceeds as follows:

• Browser cache – The browser caches DNS records for some time. Interestingly, the OS does not tell the browser the time-to-live for each DNS record, and so the browser caches them for a fixed duration (varies between browsers, 2 – 30 minutes).
• OS cache – If the browser cache does not contain the desired record, the browser makes a system call (gethostbyname in Windows). The OS has its own cache.
• Router cache – The request continues on to your router, which typically has its own DNS cache.
• ISP DNS cache – The next place checked is the cache ISP’s DNS server. With a cache, naturally.
• Recursive search – Your ISP’s DNS server begins a recursive search, from the root nameserver, through the .com top-level nameserver, to Facebook’s nameserver. Normally, the DNS server will have names of the .com nameservers in cache, and so a hit to the root nameserver will not be necessary.

3. The browser sends a HTTP request to the web server

You can be pretty sure that Facebook’s homepage will not be served from the browser cache because dynamic pages expire either very quickly or immediately (expiry date set to past). So, the browser will send this request to the Facebook server: GET http://facebook.com/ HTTP/1.1 Accept: application/x-ms-application, image/jpeg, application/xaml+xml, [...] User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; [...] Accept-Encoding: gzip, deflate Connection: Keep-Alive Host: facebook.com Cookie: datr=1265876274-[...]; locale=en_US; lsd=WW[...]; c_user=2101[...] The GET request names the URL to fetch: “http://facebook.com/”. The browser identifies itself (User-Agentheader), and states what types of responses it will accept (Accept and Accept-Encoding headers). TheConnection header asks the server to keep the TCP connection open for further requests. The request also contains the cookies that the browser has for this domain. And so the cookies store the name of the logged-in user, a secret number that was assigned to the user by the server, some of user’s settings, etc. The cookies will be stored in a text file on the client, and sent to the server with every request.

 4. The facebook server responds with a permanent redirect 

This is the response that the Facebook server sent back to the browser request: imageHTTP/1.1 301 Moved Permanently Cache-Control: private, no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Expires: Sat, 01 Jan 2000 00:00:00 GMT Location: http://www.facebook.com/ P3P: CP="DSP LAW" Pragma: no-cache Set-Cookie: made_write_conn=deleted; expires=Thu, 12-Feb-2009 05:09:50 GMT; path=/; domain=.facebook.com; httponly Content-Type: text/html; charset=utf-8 X-Cnection: close Date: Fri, 12 Feb 2010 05:09:51 GMT Content-Length: 0 The server responded with a 301 Moved Permanently response to tell the browser to go to “http://www.facebook.com/” instead of “http://facebook.com/”. 

 5. The browser follows the redirect 

The browser now knows that “http://www.facebook.com/” is the correct URL to go to, and so it sends out another GET request: GET http://www.facebook.com/ HTTP/1.1 Accept: application/x-ms-application, image/jpeg, application/xaml+xml, [...] Accept-Language: en-US User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; [...] Accept-Encoding: gzip, deflate Connection: Keep-Alive Cookie: lsd=XW[...]; c_user=21[...]; x-referer=[...] Host: www.facebook.com The meaning of the headers is the same as for the first request.

 6. The server ‘handles’ the request 

 The server will receive the GET request, process it, and send back a response. imageThis may seem like a straightforward task, but in fact there is a lot of interesting stuff that happens here – even on a simple site like my blog, let alone on a massively scalable site like facebook. Web server softwareThe web server software (e.g., IIS or Apache) receives the HTTP request and decides which request handler should be executed to handle this request. A request handler is a program (in ASP.NET, PHP, Ruby, …) that reads the request and generates the HTML for the response. Request handlerThe request handler reads the request, its parameters, and cookies. It will read and possibly update some data stored on the server. Then, the request handler will generate a HTML response. 

 7. The server sends back a HTML response 

 Here is the response that the server generated and sent back: HTTP/1.1 200 OK Cache-Control: private, no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Expires: Sat, 01 Jan 2000 00:00:00 GMT P3P: CP="DSP LAW" Pragma: no-cache Content-Encoding: gzip Content-Type: text/html; charset=utf-8 X-Cnection: close Transfer-Encoding: chunked Date: Fri, 12 Feb 2010 09:05:55 GMT The entire response is 36 kB, the bulk of them in the byte blob at the end that I trimmed. The Content-Encoding header tells the browser that the response body is compressed using the gzip algorithm. After decompressing the blob, you’ll see the HTML you’d expect: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en" id="facebook" class=" no_js"> <head> <meta http-equiv="Content-type" content="text/html; charset=utf-8" /> <meta http-equiv="Content-language" content="en" /> ... In addition to compression, headers specify whether and how to cache the page, any cookies to set (none in this response), privacy information, etc. 

 8. The browser begins rendering the HTML 

 Even before the browser has received the entire HTML document, it begins rendering the website: 

 9. The browser sends requests for objects embedded in HTML 

 As the browser renders the HTML, it will notice tags that require fetching of other URLs. The browser will send a GET request to retrieve each of these files. Here are a few URLs that my visit to facebook.com retrieved: Imageshttp://static.ak.fbcdn.net/rsrc.php/z12E0/hash/8q2anwu7.gif http://static.ak.fbcdn.net/rsrc.php/zBS5C/hash/7hwy7at6.gif … CSS style sheetshttp://static.ak.fbcdn.net/rsrc.php/z448Z/hash/2plh8s4n.css http://static.ak.fbcdn.net/rsrc.php/zANE1/hash/cvtutcee.css … JavaScript files http://static.ak.fbcdn.net/rsrc.php/zEMOA/hash/c8yzb6ub.js http://static.ak.fbcdn.net/rsrc.php/z6R9L/hash/cq2lgbs8.js 

 10. The browser sends further asynchronous (AJAX) requests 

 In the spirit of Web 2.0, the client continues to communicate with the server even after the page is rendered. For example, Facebook chat will continue to update the list of your logged in friends as they come and go. To update the list of your logged-in friends, the JavaScript executing in your browser has to send an asynchronous request to the server. The asynchronous request is a programmatically constructed GET or POST request that goes to a special URL. In the Facebook example, the client sends a POST request to http://www.facebook.com/ajax/chat/buddy_list.php to fetch the list of your friends who are online. This pattern is sometimes referred to as “AJAX”, which stands for “Asynchronous JavaScript And XML”, even though there is no particular reason why the server has to format the response as XML. For example, Facebook returns snippets of JavaScript code in response to asynchronous requests. 

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