Constants / Literals in C++

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C++ Constants :

• Constants are named locations in memory that are used to hold a value that cannot be modified by the program.

• Constants remain unchanged during the execution of a program.

• const keyword is used to declare constant data.

Syntax to declare constants :

const data_type identifier = value;

EXAMPLE:
const float PI = 3.14f;

Type of constants in C++ :

    C++ constants can be divided into two major categories :

   1. Primary Constants
   2. Secondary Constants

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Literals :

• A C++ literal is a sequence of characters (digits, letters, and other characters) that represents constant value to be stored in a variable.

• C++ specifies five major types of literals :

1. Integer Literals

2. Floating-Point Literals

3. Character Literals

4. String Literals

5. Boolean Literals

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Integer Literals :

There are three ways to represent integer number in the C++ language :

1. Decimal ( base 10 )

   int x = 20;

2. Octal ( base 8 )

   int x = 076; (starts with 0)

3. Hexadecimal ( base 16 )

   int x = 0x13A; (starts with 0x)

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Floating-Point Literals :

A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form.

Example

3.143
23123E-2L

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Character Literals :

• A character literal is represented by a single character in single quotes.

  Example:

  char c = 'a';
  char x = '@';
  
  

• If the literal begins with L (uppercase only), it is a wide character literal (e.g., L'x') and should be stored in wchar_t type of variable .

• A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a unicode character (starts with \u) (e.g., '\u02C0').

• C++allows us to have certain non graphic characters in character constants.Non graphic characters are those characters that cannot be typed directly from keyboard, for example, tabs, carriage return, etc.

• These non graphic characters can be represented by using escape sequences represented by a backslash(\) followed by one or more characters.

  Escape Sequence	Description
  \a	Alert
  \b	Backspace
  \f	Formfeed
  \n	Newline
  \r	Carriage return
  \t	Horizontal tab
  \v	Vertical tab
  \\	Backslash
  \"	Double quotation
  \'	Single quotation
  \?	Question Mark

  Example :

  #include < iostream >
  int main()
  {
  cout <<"Hello\nfrom programe.";
  return(0);
  }
  

  OUTPUT:

  Hello
  from programe.
  

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String Literals :

String literals are enclosed in double quotes.

Example :

"hello world"
"C++ prowess"

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Boolean Literals :

There are two Boolean literals and they are part of standard C++ keywords:

• true
• false

Example :

bool b = true;
bool b = false;

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Next topic is Storage Classes in C++

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