C++ Basics Tutorial 5Constants

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

All represent same number

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