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1.1 Introduction

C was developed by Dennis Ritchie at the Bell Laboratories in the early 1970s. C was initially used for system programming. Operating Systems,  Interpreters, Editors, Assembly programs are usually called systems programs. The Unix Operating System was developed using C. There are C compilers available for all computers.
- C is a middle level language
- C is a structured language
- C allows compartmentalization of code & data.

1.2 The C Program Structure

C has very few keywords, 32 to be precise. Some rules, which hold for all programs in C, are as follows:
- All keywords use lower case letters.
- C is case sensitive, India is different from INDIA.
- main() is always first function called.
 
main()
 {
 /* This is sample C program */
 int a=0;
 a = a + 1;
}

1.2.1 Function Definition

C programs divided into units called functions. The sample code has only one function main(). The function name is always followed by parenthesis. The parenthesis may contain parameters.

1.2.2 Delimiters

The function definition is always followed by an open curly brace({) and end with closing curly(}) brace. These curly braces are known as delimiters.

1.2.3 Statement Terminator


Semicolon (;) is known as Statement Terminator. It is used for terminate any statement.

1.2.4 Comment Lines

/* and */ is known as comment lines in C program. As in example.

1.3 The C Library

All C compilers provide a standard library of functions that perform the common tasks. In some implementations of C, the library exists in one large file while in others it is contained a numerous small files .A function written by a programmer can be placed in the library and be used in programs as and when required.

1.4 Data Types in C

C has four basic data types.
- char type holds one character and occupies one byte of space. (%c)
- int is an integer, typically representing the natural size of integers. (%d)
- float and double are used for floating point numbers. float occupies 4 bytes and can hold numbers with 6 digit of precision, whereas double occupies 8 bytes and can hold numbers with ten digits of precision. (%f)
- void is also a data type which holds empty set of values.

1.4.1 Modifiers used with Basic Types

- signed/unsigned type
- long/short type

1.5 Identifier Names

The name of variables, functions, labels, and various other user defined objects are called identifiers. The identifiers can contain one or more characters. It is compulsory that the first character of the identifier is a letter or an underscore. Identifiers are also case sensitive.

1.6 Variables

Variables are the named location in memory that are used to hold a value that may be modified by the C program. Variable should be declared before they can be used.
  type  variable_name;
where type is a valid data type and variable name is a valid name.

1.7 Assignment Operator

variable_name = expression;
(=) is known as assignment operator and is used to assign a value in to variable. For e.g
   a   =  2;
   a  =  b   =  c  =   2; (Multiple assignment)

1.8 Arithmetic Operators

Arithmetic operators are classified into unary and binary operators.

1.8.1 Unary Operator

 Unary operators work on only single operand.
    -   Unary minus
    ++ Increment Operator
    -- Decrement Operator

1.8.2 Binary Operator

 Binary operators work on two operands.
    + Addition
    - Subtraction
    * Multiplication
    / Division
    % Modulus

1.9 Arithmetic Expressions

   a   *   (b+c/d) * 22
   ++i   %   7
1.9.1 Precedence of Operators

 Unary   -  ++  --    Right to Left
 Binary  *    /   %    Left to Right
 Binary  + -   Left to Right
 Binary  =  Right to Left

1.10 Relational & Logical Operators

   >      Greater than
   <=    Greater than or equal
   <      Less than
   <=   Less than or equal
   ==   Equal
  ! =     Not Equal 

  Logical Operators
   &&     AND
   ||      OR
    !     NOT

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