C Tutorial

The C is a general-purpose, procedural, imperative computer programming language developed in 1972 by Dennis M. Ritchie at the Bell Telephone Laboratories to develop the UNIX operating system.

The C is the most widely used computer language, it keeps fluctuating at number one scale of popularity along with Java programming language, which is also equally popular and most widely used among modern software programmers.

C Language - Overview

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. The 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 Institute (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 softwares have been implemented using C.
Today's most popular Linux OS and RBDMS MySQL have been written in C.

Why to use C?

C was initially used for system development work, in particular the programs that make-up the operating system. C was adopted as a system development language because it produces code that runs nearly as fast as code written in assembly language. Some examples of the use of C might be:

Operating Systems
Language Compilers
Assemblers
Text Editors
Print Spoolers
Network Drivers
Modern Programs
Databases
Language Interpreters
Utilities

C Programs

A C program can vary from 3 lines to millions of lines and it should be written into one or more text files with extension ".c"; for example, hello.c. You can use "vi", "vim" or any other text editor to write your C program into a file.

This tutorial assumes that you know how to edit a text file and how to write source code inside a program file.

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":

#include <stdio.h>

int main()
{
   /* my first program in C */
   printf("Hello, World! \n");
   
   return 0;
}

Let us look various parts of the above program:

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.
The next line int main() is the main function where program execution begins.
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.
The next line printf(...) is another function available in C which causes the message "Hello, World!" to be displayed on the screen.
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:

Open a text editor and add the above-mentioned code.
Save the file as hello.c
Open a command prompt and go to the directory where you saved the file.
Type gcc hello.c and press enter to compile your code.
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.
Now, type a.out to execute your program.
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 cannot have comments within 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 refer 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:

S.N.	Types and Description
1	Basic Types: They are arithmetic types and consists of the two types: (a) integer types and (b) floating-point 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, whereas, other types will be covered in the upcoming chapters.

Integer Types

Following table gives you details 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	-32,768 to 32,767 or -2,147,483,648 to 2,147,483,647
unsigned int	2 or 4 bytes	0 to 65,535 or 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 sizeofoperator. The expressions sizeof(type) yields the storage size of the object or type in bytes. Following is an example to get the size of int type on any machine:

#include <stdio.h>
#include <limits.h>

int main()
{
   printf("Storage size for int : %d \n", sizeof(int));
   
   return 0;
}

When you compile and execute the above program it produces the following result on Linux:

Storage size for int : 4

Floating-Point Types

Following table gives you details about standard floating-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. Following example will print storage space taken by a float type and its range values:

#include <stdio.h>
#include <float.h>

int main()
{
   printf("Storage size for float : %d \n", sizeof(float));
   printf("Minimum float positive value: %E\n", FLT_MIN );
   printf("Maximum float positive value: %E\n", FLT_MAX );
   printf("Precision value: %d\n", FLT_DIG );
   
   return 0;
}

When you compile and execute the above program, it produces the following result on Linux:

Storage size for float : 4
Minimum float positive value: 1.175494E-38
Maximum float positive value: 3.402823E+38
Precision value: 6

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 which 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 which 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 the upcoming chapters.

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