2.2
Types
of Data
A C program is composed of a sequence
of characters that are grouped by a compiler into identifiable tokens. These tokens can be classified
as literals, identifiers, and keywords.
11
Chapter
2
2.2.1
Literals
Literals are classified under numeric
and non-numeric literals.
2.2.1.1
Numeric Literals
Numeric literals can be further
subdivided into whole numbers and real numbers.
Whole numbers are also called integers. These types of numbers do not
contain any fractional part and it should not have a decimal point. Real
numbers, on the other hand, are also called floating
point numbers. These numbers have fractional parts and it could also be
expressed using scientific notation.
Exponential representation may be
used to represent real numbers. An exponential representation consists of an
integer or real value followed by e
then an integer value in the exponential base 10.
Example.
2.5e2 is the same as 2.5 x 102, which
is equivalent to 250.0
2e4 is the same as 2 x 104, which is
equivalent to 20000.0
2e0 is the same as 2 x 100, which is
equivalent to 2.0
2.e5 is the same as 2.0 x 105, which
is equivalent to 200000.0
In defining numeric literals, the
following rules should be followed: 1. No
comma.
2. No space between the unary sign (+
or -) and the digits.
3. Must begin and end with a digit.
2.2.1.2
Non-Numeric Literals
Non-numeric literals may be in the
form of a character or a series of characters. A series of characters is called
a string. A string should be enclosed in double quotes, while a character is
enclosed in single quotes. Some special characters may be used, but it should
be preceded by the escape character (backslash).
Example.
‘a’
‘I’
‘+’
‘2’
“De La Salle University”
“a string with double quotes \u8221?
within”
“a single backslash \ is in this
string”
12
Overview
to C Language
Other escape characters are listed
below.
Escape
Character
Meaning
alert
tab
null
character
\u8217?
single quote
percent
symbol
2.2.2
Identifiers
Identifiers are composed of a
sequence of letters, digits, and the special character _
(underscore). Identifiers are defined
by the programmer, thus they should be descriptive. Avoid using names that are
too short or too long. Limit the identifiers from 8 to 15 characters only.
Some rules must be followed for
defining identifiers. They are as follows: 1. It must consist only of letters,
digits, and underscores.
Correct Example
Incorrect Example
_duh x-1
thisisanidentifier2 num#
a large
num
num_1 y?
2. An identifier cannot begin with a
digit.
Incorrect Identifier
1name
3to4
3. An identifier defined in the C
standard library should not be redefined.
Incorrect Identifier
printf
scanf
4. Identifiers are case sensitive;
meaning uppercase is not equal to the lowercase.
Example. ans
≠ Ans ≠ aNs ≠ anS ≠ ANs ≠ ANS
13
Chapter
2
2.2.2.1
Variables
Variables are identifiers that can
store a value that can be changed. These can be of different data types. They
can store literals or some type of structured data.
Structured data can contain one or
more values or data.
2.2.2.2
Constants
Constants are identifiers that can
store a value that cannot be changed. Usually, constant identifiers are all
capital letters with underscores between each word to distinguish them from
variables.
2.2.3
Keywords
Keywords are words that have a strict
meaning in C. These are special words
“reserved” by the programming
language for processing, thus these may not be redefined by the programmer.
Some keywords are listed below.
auto double
int struct
break else long switch
case enum
register
typedef
char extern
return
union
const float short unsigned
continue for
signed void
default goto
sizeof volatile
do if static
while
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