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C++ Programming Tutorials
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
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