DATA TYPES

 "Data types specifies the type and size of data . "

A program contains different types of data (integer , real , character etc.)  and need to store values being used in the program . C++ language is rich of data types . 

It is divided into three types ------------------

1. Primary data types 
2. Derived data types 
3. User Defined data types

Data Type	Size (in bytes)	Range
short int	2	-32,768 to 32,767
unsigned short int	2	0 to 65,535
unsigned int	4	0 to 4,294,967,295
int	4	-2,147,483,648 to 2,147,483,647
long int	4	-2,147,483,648 to 2,147,483,647
unsigned long int	4	0 to 4,294,967,295
long long int	8	-(2^63) to (2^63)-1
unsigned long long int	8	0 to 18,446,744,073,709,551,615
signed char	1	-128 to 127
unsigned char	1	0 to 255
float	4
double	8
long double	12
wchar_t	2 or 4	1 wide character

VARIABLE IN C++

A variable is a value that can change anytime . It is a memory location used to store a data value . variable name is case sensitive.

1. They must always begin with a letter , although some system permit underscore as the first character.
2. The length of a variable most not be more than 8 character.
3. white space is not allowed .
4. a variable should not be a keyword.
5. it should not contain any special characters.

example of invalid variable names are :

 

123 , (area) , -hello , %abc , etc.

A variable must be declared before it can be used . Variables can be declared at the start of any block of code . 

constant in c++ language |

 " A constant value is the one which does not change during the execution of a program . "

constant uses a secondary storage area .

constant has fixed value .

constant in every language are the same .

in C++ language constant are of two types ___

1. numeric constant
2. non-numeric constant

Identifier in C++ |

 the name of a variable , function , class , or other entity in c++ is called an identifier.

rules :  

•  The identifier can not be a keyword . Keywords are reserved .
• The identifier can only be composed letters, number , and the underscore character . that means the name can not contains symbols nor whitespace .
• The identifier must begin with a letter or an underscore . it can not start with a number ,
• C++ distinguishes between lower and upper case letter . 

 

Keywords in C++ |

 Every words in C++ language is a keyword or an identifier . Keywords in C++ language can not be used as a variable name . They are specifically used by the compiler for its own purpose and they serve as   building blocks of a C++ program.

 C++ language has some reserve word which are called keywords. They are the part of the C++ tokens.

There are 63 keywords currently defined for standard C++. 

C++ Keyword
asm	double	new	switch
auto	else	operator	template
break	enum	private	this
case	extern	protected	throw
catch	float	public	try
char	for	register	typedef
class	friend	return	union
const	goto	short	unsigned
continue	if	signed	virtual
default	inline	sizeof	void
delete	int	static	volatile
do	long	struct	while

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