Character set, variables, constants and keywords

Character set:
Character set contains alphabets, numbers, and symbols for representing information. Following set shows characters used in C:

Alphabets	A,B,C,D……………X,Y,Z A,b,c,d…………….x,y,z
Numbers	0,1,2,3,4,5,6,7,8,9
Special Symbols	?></.,;’:”[]{}\|*-+_()*&^%$#@!

Variables:

Variable is an entity which can change or it is a name of the memory location. It should start with only alphabets or underscore. Also called identifiers.

e.g.  int A=10;

consider memory location 1000 in a computer’s memory where 10 value is stored. So we can retrieve or modify value 10 through variable A.

       

Constants:

Constant is an entity which cannot change.

e.g. int A=10; 10 is a constant.

Types of constants:

1.Primary Constants

2.Secondary Constants

Constants	Range
Integer	-32768 to +32767
Float	-3.4e38 to +3.4e38
Character	-128 to 127

Integer constant:

e.g int A=10, B=32768;

In given example, B has value out of range of integer constant so

Float constant:

e.g float f=2.3e+20;

2.3e+20=2.3*10²⁰

Character constant:

Character constant consist only single alphabet, number or special symbol enclosed in a single inverted comma.

e.g. char A=’3’; 

Keywords:
Keywords are reserved words whose meaning is known to the compiler. Keywords should be in lower case. There are 32 keywords in C language:

void	return	int	case
double	public	char	long
goto	for	while	static
unsigned	switch	break	union
auto	volatile	struct	continue
sizeof	if	else	const
float	short	signed	default
typedef	enum	extern	do