Constants

Constants are expressions with a fixed value.

Literals

Literals are used to express particular values within the source code of a
program. We have already used these previously to give concrete values to
variables or to express messages we wanted our programs to print out, for
example, when we wrote:

the 5 in this piece of code was a literal constant.

Literal constants can be divided in Integer Numerals, Floating-Point Numerals,
Characters, Strings and Boolean Values.

Integer Numerals

They are numerical constants that identify integer decimal
values. Notice that to express a numerical constant we do not have to write
quotes (") nor any special character. There is no doubt that it is a constant:
whenever we write 1776 in a program, we will be referring to the value 1776.

In addition to decimal numbers (those that all of us are used to use every day)
C++ allows the use as literal constants of octal numbers (base 8) and
hexadecimal numbers (base 16). If we want to express an octal number we have to
precede it with a 0 (zero character). And in order to express a hexadecimal
number we have to precede it with the characters 0x (zero, x). For example, the
following literal constants are all equivalent to each other:

75
// decimal
0113 // octal
0x4b // hexadecimal |

All of these represent the same number: 75 (seventy-five)
expressed as a base-10 numeral, octal numeral and hexadecimal numeral,
respectively.

Literal constants, like variables, are considered to have a specific data type.
By default, integer literals are of type int. However, we can force them to
either be unsigned by appending the u character to it, or long by appending l:

75
// int
75u // unsigned int
75l // long
75ul // unsigned long |

In both cases, the suffix can be specified using either upper
or lowercase letters.

Floating Point Numbers

They express numbers with decimals and/or exponents. They can include either a
decimal point, an e character (that expresses "by ten at the Xth height", where
X is an integer value that follows the e character), or both a decimal point and
an e character:

3.14159 //
3.14159
6.02e23 // 6.02 x 10^23
1.6e-19 // 1.6 x 10-19
3.0
// 3.0 |

These are four valid numbers with decimals expressed in C++.
The first number is PI, the second one is the number of Avogadro, the third is
the electric charge of an electron (an extremely small number) -all of them
approximated- and the last one is the number three expressed as a floating-point
numeric literal.

The default type for floating point literals is double. If you explicitly want
to express a float or long double numerical literal, you can use the f or l
suffixes respectively:

3.14159L
// long double
6.02e23f // float |

Any of the letters than can be part of a floating-point
numerical constant (e, f, l) can be written using either lower or uppercase
letters without any difference in their meanings.

NEXT >> Character
and String Literals

Have a Question ?
post your questions here. It
will be answered as soon as possible.

Check
C Aptitude Questions
for more C Aptitude Interview Questions with Answers

Check
C Interview Questions
for more C Interview Questions with Answers.