C - Language

C is a general purpose high level language that was originally developed by Dennis M. Ritchie to develop the Unix operating system at Bell Labs. C was originally first implemented on the DEC PDP-11 computer in 1972.

In 1978, Brian Kernighan and Dennis Ritchie produced the first publicly available description of C, now known as the K&R standard.

The UNIX operating system, the C compiler, and essentially all UNIX applications programs have been written in C. C has now become a widely used professional language for various reasons.

• Easy to learn
• Structured language
• It produces efficient programs.
• It can handle low-level activities.
• It can be compiled on a variety of computer platforms.

Facts about C

• C was invented to write an operating system called UNIX.
• C is a successor of B language which was introduced around 1970
• The language was formalized in 1988 by the American National Standard Institue (ANSI).
• The UNIX OS was totally written in C By 1973.
• Today C is the most widely used and popular System Programming Language.
• Most of the state of the art software have been implemented using C.
• Today's most popular Linux OS and RBDMS MySQL have been written in C.

C - Environment Setup

Before you start doing programming using C programming language, you need following two software's available on your computer, (a) Text Editor and (b) The C Compiler.

Text Editor:

This will be used to type your program. Examples of few editors include Windows Notepad, OS Edit command, Brief, Epsilon, EMACS, and vim or vi
Name and version of text editor can vary on different operating systems. For exampe Notepad will be used on Windows and vim or vi can be used on windows as well as Linux, or Unix.
The files you create with your editor are called source files and contain program source code. The source files for C programs are typically named with the extension .c.
Before starting your programming, make sure you have one text editor in place and you have enough experience to write a computer program, save it in a file, compile it and finally execute it.

The C Compiler:

The source code written in source file is the human readable source for your program. It needs to be "compiled", to turn into machine language so that your cpu can actually execute the program as per instructions given.
This C programming language compiler will be used to compile your source code into final executable program. I assume you have basic knowledge about a programming language compiler.
Most frequently used and free available compiler is GNU C/C++ compiler, otherwise you can have compilers either from HP or Solaris if you have respective Operating Systems.
Following section guides you on how to install GNU C/C++ compiler on various OS. I'm mentioning C/C++ together because GNU gcc compiler works for both C and C++ programming languages.

Installation on Unix/Linux

If you are using Linux or Unix then check whether GCC is installed on your system by entering the following command from the command line:
$ gcc -v
If you have GNU compiler installed on your machine then it should print a message something as follows:
Using built-in specs. Target: i386-redhat-linux Configured with: ../configure --prefix=/usr ....... Thread model: posix gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)
If GCC is not installed, then you will have to install it yourself using the detailed instructions available at http://gcc.gnu.org/install/
This tutorial has been written based on Linux and all the given examples have been compiled on Cent OS flavour of Linux system.

Installation on Mac OS

If you use Mac OS X, the easiest way to obtain GCC is to download the Xcode development environment from Apple's web site and follow the simple installation instructions. Once you have Xcode setup, you will be able to use GNU compiler for C/C++.
Xcode is currently available at developer.apple.com/technologies/tools/.

Installation on Windows

To install GCC at Windows you need to install MinGW. To install MinGW, go to the MinGW homepage, www.mingw.org, and follow the link to the MinGW download page. Download the latest version of the MinGW installation program, which should be named MinGW- .exe.
While installing MinWG, at a minimum, you must install gcc-core, gcc-g++, binutils, and the MinGW runtime, but you may wish to install more.
Add the bin subdirectory of your MinGW installation to your PATH environment variable so that you can specify these tools on the command line by their simple names.
When the installation is complete, you will be able to run gcc, g++, ar, ranlib, dlltool, and several other GNU tools from the Windows command line. 

C - Program Structure

Before we study basic building blocks of the C programming language, let us look a bare minimum C program structure so that we can take it as a reference in upcoming chapters.

C Hello World Example 

A C program basically consists of the following parts:

• Preprocessor Commands
• Functions
• Variables
• Statements & Expressions
• Comments

Let us look at a simple code that would print the words "Hello World":

Let us look various parts of the above program:
 1. The first line of the program #include <stdio.h> is a preprocessor command which tells a
C compiler to include stdio.h file before going to actual compilation.
2. The next line int main() is the main function where program execution begins.
3. The next line /*...*/ will be ignored by the compiler and it has been put to add additional
comments in the program. So such lines are called comments in the program.
4. The next line printf(...) is another function available in C which causes the message
"Hello, World!" to be displayed on the screen.
5. The next line return 0; terminates main()function and returns the value 0.

Compile & Execute C Program:

Lets look at how to save the source code in a file, and how to compile and run it. Following are
the simple steps:
1. Open a text editor and add the above mentioned code.
2. Save the file as hello.c
3. Open a command prompt and go to the directory where you saved the file.
4. Type gcc hello.c and press enter to compile your code.
5. If there are no errors in your code the command prompt will take you to the next line and
would generate a.out executable file.
6. Now type a.out to execute your program.
7. You will be able to see "Hello World" printed on the screen
$ gcc hello.c
$ ./a.out
Hello, World!
Make sure that gcc compiler is in your path and that you are running it in the directory
containing source file hello.c.

C - Basic Syntax

You have seen a basic structure of C program, so it will be easy to understand other basic
building blocks of the C programming language.

Tokens in C

A C program consists of various tokens and a token is either a keyword, an identifier, a constant,
a string literal, or a symbol. For example, the following C statement consists of five tokens:
printf("Hello, World! \n");
The individual tokens are:
printf
(
"Hello, World! \n"
)
;

Semicolons ;

In C program, the semicolon is a statement terminator. That is, each individual statement must be
ended with a semicolon. It indicates the end of one logical entity.
For example, following are two different statements:
printf("Hello, World! \n");
return 0;

Comments

Comments are like helping text in your C program and they are ignored by the compiler. They
start with /* and terminates with the characters */ as shown below:
/* my first program in C */
You can not have comments with in comments and they do not occur within a string or character
literals.

Identifiers

A C identifier is a name used to identify a variable, function, or any other user-defined item. An
identifier starts with a letter A to Z or a to z or an underscore _ followed by zero or more letters,
underscores, and digits (0 to 9).
C does not allow punctuation characters such as @, $, and % within identifiers. C is a case
sensitive programming language. Thus Manpower and manpower are two different identifiers in
C. Here are some examples of acceptable identifiers:
mohd zara abc move_name a_123
myname50 _temp j a23b9 retVal

Keywords

The following list shows the reserved words in C. These reserved words may not be used as
constant or variable or any other identifier names.
auto else long switch
break enum register typedef
case extern return union
char float short unsigned
const for signed void
continue goto sizeof volatile
default if static while
do int struct _Packed
double

Whitespace in C

A line containing only whitespace, possibly with a comment, is known as a blank line, and a C
compiler totally ignores it.
Whitespace is the term used in C to describe blanks, tabs, newline characters and comments.
Whitespace separates one part of a statement from another and enables the compiler to identify
where one element in a statement, such as int, ends and the next element begins. Therefore, in
the following statement:
int age;
There must be at least one whitespace character (usually a space) between int and age for the
compiler to be able to distinguish them. On the other hand, in the following statement
fruit = apples + oranges; // get the total fruit
No whitespace characters are necessary between fruit and =, or between = and apples, although
you are free to include some if you wish for readability purpose.

C - Data Types

In the C programming language, data types refers to an extensive system used for declaring
variables or functions of different types. The type of a variable determines how much space it
occupies in storage and how the bit pattern stored is interpreted.

The types in C can be classified as follows:

 Types and Description

1. Basic Types: They are arithmetic types and consists of the two types: (a) integer types and (b) floatingpoint types.
2. Enumerated types: They are again arithmetic types and they are used to define variables that can only be assigned certain discrete integer values throughout the program.
3. The type void: The type specifier void indicates that no value is available.
4. Derived types: They include (a) Pointer types, (b) Array types, (c) Structure types, (d) Union types and (e) Function types.
The array types and structure types are referred to collectively as the aggregate types. The type of a function specifies the type of the function's return value. We will see basic types in the following section where as other types will be covered in the upcoming chapters.

Integer Types

Following table gives you detail about standard integer types with its storage sizes and value
ranges:

Type                                             Storage size                     Value range
char                                              1 byte                             -128 to 127 or 0 to 255
unsigned char                                1 byte                              0 to 255
signed char                                   1 byte                            -128 to 127
int                                                 2 or 4 bytes                   -2,147,483,648 to 2,147,483,647
unsigned int                                   2 or 4 bytes                    0 to 4,294,967,295
short                                             2 bytes                          -32,768 to 32,767
unsigned short                               2 bytes                           0 to 65,535
long                                              4 bytes                           -2,147,483,648 to 2,147,483,647
unsigned long                                4 bytes                            0 to 4,294,967,295

To get the exact size of a type or a variable on a particular platform, you can use the sizeof
operator. The expressions sizeof(type) yields the storage size of the object or type in bytes.

Floating-Point Types

Following table gives you detail about standard float-point types with storage sizes and value
ranges and their precision:
Type                                           Storage size                      Value range Precision
float                                            4 byte                               1.2E-38 to 3.4E+38 6 decimal places
double                                        8 byte                               2.3E-308 to 1.7E+308 15 decimal places
long double                                10 byte                              3.4E-4932 to 1.1E+4932 19 decimal places

The header file float.h defines macros that allow you to use these values and other details about
the binary representation of real numbers in your programs.

The void Type

The void type specifies that no value is available. It is used in three kinds of situations:

S.N.        Types and Description
1              Function returns as void:  There are various functions in C who do not return value or you can say they return void. A function with no return value has the return type as void. For example void exit (int
status);

2             Function arguments as void:  There are various functions in C who do not accept any parameter. A function with no parameter can accept as a void. For example int rand(void);

3             Pointers to void:  A pointer of type void * represents the address of an object, but not its type. For example a memory allocation function void *malloc( size_t size ); returns a pointer to void which can
be casted to any data type.

 The void type may not be understood to you at this point, so let us proceed and we will cover these concepts in upcoming chapters.

C - Variables

A variable is nothing but a name given to a storage area that our programs can manipulate. Each
variable in C has a specific type, which determines the size and layout of the variable's memory;
the range of values that can be stored within that memory; and the set of operations that can be
applied to the variable.

The name of a variable can be composed of letters, digits, and the underscore character. It must
begin with either a letter or an underscore. Upper and lowercase letters are distinct because C is
case-sensitive. Based on the basic types explained in previous chapter, there will be following
basic variable types:

Type           Description
char            Typically a single octet(one byte). This is an integer type.
int               The most natural size of integer for the machine.
float            A single-precision floating point value.
double        A double-precision floating point value.
void            Represents the absence of type.

C programming language also allows to define various other type of variables which we will
cover in subsequent chapters like Enumeration, Pointer, Array, Structure, Union etc. For this
chapter, let us study only basic variable types.

Variable Declaration in C

All variables must be declared before we use them in C program, although certain declarations
can be made implicitly by content. A declaration specifies a type, and contains a list of one or
more variables of that type as follows:

type variable_list;

Here, type must be a valid C data type including char, int, float, double, or any user defined data
type etc., and variable_list may consist of one or more identifier names separated by commas.
Some valid variable declarations are shown here:

int i, j, k;
char c, ch;
float f, salary;
double d;

A variable declaration does not allocate any memory space for the variable but a variable
definition allocate required memory space for that variable. A variable declaration with an initial
value as shown below will become variable definition and required memory is allocated for the
variable.

int i = 100;

An extern declaration is not a definition and does not allocate storage. In effect, it claims that a
definition of the variable exists some where else in the program. A variable can be declared
multiple times in a program, but it must be defined only once. Following is the declaration of a
variable with extern keyword:

extern int i;

Variable Initialization in C

Variables are initialized (assigned an value) with an equal sign followed by a constant
expression. The general form of initialization is:

variable_name = value;

Variables can be initialized (assigned an initial value) in their declaration. The initializer consists
of an equal sign followed by a constant expression as follows:

type variable_name = value;

Some examples are:

int d = 3, f = 5;                          /* initializing d and f. */
byte z = 22;                              /* initializes z. */
double pi = 3.14159;               /* declares an approximation of pi. */
char x = 'x';                             /* the variable x has the value 'x'. */

It is a good programming practice to initialize variables properly otherwise, sometime program
would produce unexpected result.

Lvalues and Rvalues in C:

There are two kinds of expressions in C:
1. lvalue : An expression that is an lvalue may appear as either the left-hand or right-hand
side of an assignment.
2. rvalue : An expression that is an rvalue may appear on the right- but not left-hand side of
an assignment.

Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals
are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a
valid statement:

int g = 20;

But following is not a valid statement and would generate compile-time error:

10 = 20;

C - Constants and Literals

The constants refer to fixed values that the program may not alter during its execution. These
fixed values are also called literals.

Constants can be of any of the basic data types like an integer constant, a floating constant, a
character constant, or a string literal. There are also enumeration constants as well.

The constants are treated just like regular variables except that their values cannot be modified
after their definition.

Integer literals

An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or
radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal.

An integer literal can also have a suffix that is a combination of U and L, for unsigned and long,
respectively. The suffix can be uppercase or lowercase and can be in any order.

Here are some examples of integer literals:

212                                      /* Legal */
215u                                    /* Legal */
0xFeeL                                /* Legal */
078                                     /* Illegal: 8 is not an octal digit */
032UU                               /* Illegal: cannot repeat a suffix */

Following are other examples of various type of Integer literals:

85                                     /* decimal */
0213                                 /* octal */
0x4b                                 /* hexadecimal */
30                                    /* int */
30u                                  /* unsigned int */
30l                                   /* long */
30ul                                 /* unsigned long */

Floating-point literals

A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent
part. You can represent floating point literals either in decimal form or exponential form.

While representing using decimal form, you must include the decimal point, the exponent, or
both and while representing using exponential form, you must include the integer part, the
fractional part, or both. The signed exponent is introduced by e or E.

Here are some examples of floating-point literals:

3.14159                         /* Legal */
314159E-5L                  /* Legal */
510E                             /* Illegal: incomplete exponent */
210f                              /* Illegal: no decimal or exponent */
.e55                              /* Illegal: missing integer or fraction */

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