Variables
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Introduction
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The defined type of memory area where
the value is stored is called variable.
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Variables are the data item whose
values may vary during the execution of the program.
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A specific location or the address in
the memory is allocated for each variable and the value of
thatvariable is stored in that location.
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These locations may be integer,
real or character etc.
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Rules for constructing variables
names
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There are some specific rules for
constructing variable names in C language:
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(a) Variable name may be a
combination of alphabet digits or underscores and
its lengths should not exceed 8 characters, some compilers
allow 40 characters also.
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(b) The first character must be
an alphabet.
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(c) No comma, blank spaces are
allowed in variable name.
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(d) No special symbols except underscore can
be used as variable names.
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Variable
declaration
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All
the variables must be declared before their use. It does two
things:
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(a)
Tell the compiler what the variable name is.
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(b)
Specify what type of data that a variable will hold.
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Syntax
of variable declaration:
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data_type
variable_name;
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Example
of variable declaration:
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int
i,j,k;
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char
ch;
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Assigning
values to variables To assign values to the variables, assignment
operator (=) is used. Syntax of assigning
values: variable declaration;Variable_name = value; Example of
assigning values: Int i , j;j = 5 ;i = 0 ; It is also possible to
assign a value at the time of declaration.e.g.int i = 5; More than one
variable can be initialized in one statement using multiple assignment
operators. e.g. j = m = 2; There could be an exception while using
multiple assignment operators. e.g. int i , j = 2 , k; here the
assignment will be i = 0 j=2 and k = garbage value.
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Scope of variables: Local &
Global
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Scope of variable means where the variable stands
in the program. All variables may not necessary be
available to all statements in a program.
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Variables can have two types of
scope:
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a) Local:
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When a variable is declared inside the function
then such a variable is known as local variable.
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A local variable can only be accessed by the
function in which it is declared. It cannot be accessed by other function.
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b) Global:
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A variable which is declared outside all functions
is known as global variable.
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A variable with a global scope is accessible to all
the statements in the program. A global variablecan
be accessed by all the functions.
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Constants
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Introduction
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There are some values which do not change during the execution of
the program. These values are called constants.
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Constants are of fixed value that
remain unchanged during the execution of a program, and are used in
assignment of statements. Constants are stored in
variables.
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Syntax of constant declaration:
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Const datatype var_name = value;
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Example of Constant declaration:
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Const int a = 5;
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In C language there are five types of constants which
has been described separately
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Character constants
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A character constant consists of a single digit or
a single special symbol enclosed within a pair of single inverted commas.
The maximum length of a character constant can be 1 character.
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e.g. --> 'a', 'i' , '5', '='.
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There are some character sequence constants which
are used in C to represented special action, these are called C
Escape Sequence.
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List of these escape sequence and
its tasks are given below:
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\a : audible bell
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\f : form feed
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\r : carriage return
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\v : vertical tab
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\' : single quote
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\? : question mark
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\HHH: 1 to 3 digit hex value.
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\b : backspace
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\n : newline
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\t : horizontal tab
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\\ : backslash
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\" : double quote.
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\000 : 1 to 3 digit
octal value
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Integer constants
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An integer constant refers to a sequence of digits.
It could be either positive or negative. and must have at least one digit.
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It mustn't have a decimal point. No commas or blank are allowed
within an integer constant. The allowable range
for integer constants is -32767 to 32767.
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There are three types of integer
constants:
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1. decimal :
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In decimal notation ,simply we write decimal number. e.g. 24,678
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2. octal :
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In octal notation, write(0)immediately before the octal
represention,e.g.-076,-076
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3. hexadecimal :
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In hexadecimal notation ,the constant is preceded by
0x,e.g.,0x3e,-0x3e.
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Some example of integer constants:
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: 426
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: +762
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: -8000
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: -7605
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Real constants
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Real constants are often
called Floating Point constants.
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It has three parts:
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1. A sign (+ or -) preceding the number portion (optional).
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2. A number portion (representing the base).
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3. An exponent portion following the number portion (optional). This
starts with E or E followed by an integer. The integer may be preceded by a
sign.
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A real constant must have at least one digit. It must have a decimal
point. It could be either positive (default) or negative. No commas and
blank are allowed within a real constant.
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Some example of real constants:
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: +.72
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: +72
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: +7.6E+2
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: 24.4e-5
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Logical & String constants
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A logical constant can have either of two values
either true or false. In C a non-zero value is always treated as true
whereas zero is treated as false.
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The logical constants are very useful in evaluating
logical expressions and complex condition.
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A group of character enclosed within a pair of double inverted
commas (" ") is treated as a string
constant.
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some example of string constant:
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: "Hello"
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"Welcome to Execute Codes"
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"a"
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