C Programming Language Tutorial – I (Data types, Identifiers, Variables, Keywords, Comments, Constant, Storage classes)

Data Types

C supports several types of data, each of which may be represented differently within the computer memory. The data type specifies data in computer memory.

C provides variety of data types.

• Primitive or simple or inbuilt data types

- int, float, char, double

• Derive data types

- Array, pointer

• User define data types

- structure, typedof, enumeration

Data Type	Size(bytes)	Range
char	1	-128 to 128
int	2	-32767 to 32768
float	4	3.4e-38 to 3.4e+38
double	8	1.7e-308 to 1.7+308

Identifiers

Identifiers are the name given to various programming elements by a programmer. It is fundamental requirement of programming language.

Keywords

Keywords are the reserved identifiers and have predefined meaning to the compiler. They are always written in lower case. They cannot be use as name for user define identifier. C has 32 keywords.

auto case const default

double enum float goto

int register short sizeof

struct typedef unsigned volatile

break char continue do

else extern for if

long return signed static

switch union void while

Comments

Comments are used to enhance the readability and understanding of a program.

These are not executable statements and they are ignored by the compiler at the time of compilation.

Single line comments – (//)

Multi lines comments – (/* -----*/)

Constants

Constants are those whose value is fixed throughout the execution of program.

Each constant has a type, determined by its form and value.

·         Integer Constants – contains sequence of digit.

·         Character constants – encloses in a single quotation mark.

·         Floating constants – consists of integer part and a decimal point. It can be suffixed by f.

String Literals

It is a sequence of character surrounded by double quotation marks.

Escape Sequences

C supports some special backslash character constants that are used in output functions. These character constants are known as escape sequence characters.

Character	Escape Sequence
New line	\n
Horizontal tab	\t
Vertical tab	\v
Backspace	\b
Carriage return	\r
Form feed	\f
Backslash	\\
Single quote	\’
Double quote	\”
Question mark	\?
Bell (alarm / beep)	\a

Symbolic Constant

The constant values that have been given a name are called symbolic constants. In C you can create symbolic constants using #define. The subsequent use of symbolic constants within the program will automatically replace the specified value before the compilation of program.

Variables

Variables are named locations in memory that are used to hold a value that may be modified by the program. Every variable has two parts, a name and a data type.

Declaration of variable

Data-type varable;

int age;

char sname;

float avg;

Rules for declaration

-   Name of the variable should be start from alphabet.

-   Space is not allowed within the variable name.

-   Space is compulsory in between data type & variable name.

-   Only underscore character is allowed in variable name.

-   Variables are declared under a single data type are separated by comma.

-   Semicolon is used at the end of variable declaration.

Initializing a variable

A process of assigning value to the variable for the first time after its declaration is known as initialization.

    int no=10;

Scope of variable

·   Block scope – A variable is visible only with in the block in which it has been declared.

·   Function scope – A variable is visible to the entire function in which it has been declared.

·   File scope – A variable is visible to all the functions within a file.

Storage Class

Variables in C not only have data type, but also storage class that provides information about their location and visibility. A storage class determines the portion of a program within which the variables are accessible. C provides variety of storage classes.

·   auto – It declares an automatic variable that is visible only in the block in which it is declared.

·   static – It initialized variable to 0 unless another value is specified. A variable retains previous value between calls to the functions.

·   extern – It is accessible throughout the program. It is allocated when the program begins and deallocated when the program ends.

·   register – the register keyword specifies that the variable is to be stored in a machine register, if possible.

The volatile keyword is also use for declaration of variable which tell to compiler that the variable value is sudden change at any time.