5. Introduction to c++: Constants: Basic Programming for Beginners

Veröffentlicht am: 20 August 2012
auf dem Kanal: DigitalStage

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• 5. Introduction to c++: Constants: Basic P...
C++ Basics Tutorial 5
Constants

Topics Covered
• Literal Constants
• Defined Constants
• Declared Constants

Literal constants
• Most easy to see and most obvious constants

Types of literal constants
• Integer Numerals
• Floating-Point Numerals
• Boolean literals
• Character literals
• String literals

Integer Numerals
• A number without decimal points (duh!)
• Examples: 23, 56, 8...
• In C++, expressing numerical constants does not require any special character like "".
• Integer numerals can be defined in other numeral forms like octal or hexadecimal.
• 255 Decimal Value
• 0377 Octal value
• 0xff Hexadecimal Value

Decimal, Octal, hexadecimal, signed and unsigned representation
• To denote an octal number(Base 8 number) start the number with 0 (zero)
• To denote a hexadecimal value(base 16 number) start with 0 x (zero "x")
• Write normally for decimal numerical(base 10) system value.
• Force int to be unsigned by adding u(or U) at the end of number. (Ex: 19U) or l(or L) to make it long( 19L or 19UL)

Floating Point literals
• To represent number with decimal or exponents
• A decimal point "." or a "e" can be added to represent the number, where e means to the "power by 10" to number after e.
• Also can have both "e" and "."
• Example: 3.14 Value of Pi
5.97e24(Mass of earth) = 5.97 x 10 ^ 24
or 1.67e-27(Mass of proton) = 1.67 x 10 ^ -27
• Force number to be long double add L or l, to force number to be float add f or F in the end of the number
• E or e both are same. C++ is not case sensitive in this case.

Boolean literals
• Only two boolean literals in C++: true or false.
• Can be represented by bool data type.

Character literals
• One character. Example: 'a', 'b', 'A' etc...
• To represent character literals we put them inside single quotes. This is done to differentiate them from possible variable identifiers that we might define in the program.
• If you just write 1 it is numerical literal. But '1' makes it character literal.
• 'a' is a character literal where as just a is a variable identifier named a.

String literals
• Combination of characters.
• Inside double quotes "".
• Example "Dean"

Escape Characters
• Characters and string both can have a special character called escape character.
• Impossible or at least difficult to express otherwise
• Precede by a backslash(\) and a character.
• Example: \n  New Line, \t  Tab
• '\n' or '\t' or "LineOne\nLineTwo\nLineThree"
• "\"DoubleQuote\"" = "DoubleQuote" when you print.

Few list of escape characters:
• \n = Newline
• \t = tab
• \r = carriage return
• \v = vertical tab
• \b = backspace
• \f = form feed
• \a = alert beep
• \' = single quote(')
• \" = Double quote(")
• \? = question mark(?)
• \\ = backslash(\)

Defined constants
• Using something called preprocessor directive
• Use #define preprocessor directive
• Define constant that will be used frequently.
• Example:
#define PI 3.14159
#define NEWLINE '\n'
• This now have defined two constants called PI and NEWLINE. Now you can use PI
and NEWLINE as other constants we learned earlier.
• Due to #define the C++ compiler literally replaces all the occurrences of PI and
NEWLINE with assigned value(3.14159 or '\n')

Directive
• A directive is not a C++ statement. It is interpreted by the preprocess that
happens before even looking at the code of the program. So these directive does
not need to have a semicolon in the end.
• Directives start with #. Applies to #include as well.

Declared Constants (const)
• Using const prefix with specific data type you make a variable unchangeable
throughout the program.
• Example:
const int a = 23;
const char newline = '\n'
• The are completely regular variables except that you cannot modify these after you
initialize.

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• Next Chapter: We will talk about operators
• Then: Basic input/ output.
• End of Basics.

• Then to Control structures / Functions

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