Constants, Variables, Keywords, Data Types

C Tokens (Constants, Variables, Keywords, Data Types):

A constant is a quantity that doesn’t change. This quantity can be stored at a locations in the memory of the computer. A variable also can be stored in the memory of the computer. But the contents of the variable can be changed.

Types of C Constants:

C constants can be divided into two major categories:

1.       Primary Constants  

2.       Secondary Constants

1.      Primary Constants we learn Integer Constants, Real Constants, Character

Constants and

2.       Secondary Constants we learn Array, Pointers, Structures,

Union, Enum etc.

Rules for constructing Integer Constants:

a)       An integer constant must have at least one digit

b)       It must not have a decimal point.

c)        It can be either positive or negative.

d)       If no sign precedes an integer constant it is assumed to be positive.

e)       No commas or blanks are allowed within an integer constant.

f)        The allowable range for integer constants is -32768 to 32767.

     

   Ex: 426

          +782

          -8000

          -7605

/* program for Integer no’s   */

# include<stdio.h>

void main()

{

int a, b,c;

clrscr();

c=a+b;

printf(“value of c is %d”,c);

getch();

}

Rules for constructing Real Constants:

a)       A real constant must have at least one digit

b)       It must have a decimal point.

c)        It can be either positive or negative.

d)       If no sign precedes a real constant it is assumed to be positive.

e)       No commas or blanks are allowed within an real constant.

f)        The allowable range for  real constants is -3.4e38 to 3.4e38.

     

   Ex: +325.34

          +782.0

          -80.76

          -760.578

#include <stdio.h>

int main (void)

{

   /* declarations */

   int a;

   double x;

     /* executable statements */

   a = 1000;

   x = 100.583665;

    printf ("%d\n", a);

   printf ("%3d\n", a);

   printf ("%4d\n", a);

   printf ("%5d\n", a);

   printf ("\n");

   printf ("%lf\n", x);

   printf ("%15lf\n", x);

   printf ("%15.4lf\n", x);

   printf ("%18.2lf\n", x);

   printf ("%12.0lf\n", x);

  return (0);

}

Rules for constructing Character Constants:

a)       A character constant is a single alphabet, a single digit or a single special symbol enclosed within single inverted commas.

b)       The maximum length of a character constant can be 1 character.

     

   Ex:   ‘A’

            ‘I’

            ‘5’

            ‘=‘

/ * inputting characters
A program that asks the user for 4 characters and displays them on the screen.

#include <stdio.h>

int  main (void)

{

   /* declarations */

   char letter1, letter2, letter3, letter4;

   printf ("enter a name: ");

   scanf ("%c%c%c%c", &letter1, &letter2, &letter3, &letter4);

   printf ("you entered: %c%c%c%c", letter1, letter2, letter3, letter4);

   printf (" / backwards: %c%c%c%c\n", letter4, letter3, letter2, letter1);

     return (0);

}

output:

enter a name: lucky

you entered : lucky

C Keywords:

Keywords are the words whose meaning has already been explained to the C compiler. The keywords cannot be used as variable names. There are only 32 keywords available in C.

auto	double	if	static
break	else	int	struct
case	enum	long	switch
char	extern	near	typedef
const	float	register	union
continue	far	return	unsigned
default	for	short	Void
do	goto	signed	While

Data types in C

1. Fundamental Data Types

• Integer types
• Floating type
• Character type

2. Derived Data Types

·      Arrays

·      Pointers

·      Structures

Data types in c refer to an extensive system used for declaring variables or functions of different types. The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted.

The types in C can be classified as follows −

S.N.	Types & Description
1	Basic Types They are arithmetic types and are further classified into: (a) integer types and (b) floating-point types.
2	Enumerated types They are again arithmetic types and they are used to define variables that can only assign certain discrete integer values throughout the program.
3	The type void The type specifier void indicates that no value is available.
4	Derived types They include (a) Pointer types, (b) Array types, (c) Structure types, (d) Union types and (e) Function types.

The array types and structure types are referred collectively as the aggregate types. The type of a function specifies the type of the function's return value. We will see the basic types in the following section, where as other types will be covered in the upcoming chapters.

Integer Types

The following table provides the details of standard integer types with their storage sizes and value ranges –

Type	Storage size	Value range
char	1 byte	-128 to 127 or 0 to 255
unsigned char	1 byte	0 to 255
signed char	1 byte	-128 to 127
int	2 or 4 bytes	-32,768 to 32,767 or -2,147,483,648 to 2,147,483,647
unsigned int	2 or 4 bytes	0 to 65,535 or 0 to 4,294,967,295
short	2 bytes	-32,768 to 32,767
unsigned short	2 bytes	0 to 65,535
long	4 bytes	-2,147,483,648 to 2,147,483,647
unsigned long	4 bytes	0 to 4,294,967,295

To get the exact size of a type or a variable on a particular platform, you can use the sizeof operator. The expressions sizeof(type) yields the storage size of the object or type in bytes. Given below is an example to get the size of int type on any machine −

#include <stdio.h>

#include <limits.h>

int main() {

   printf("Storage size for int : %d \n", sizeof(int));

  

   return 0;

}

When you compile and execute the above program, it produces the following result on Linux −

Storage size for int : 4

Floating-Point Types

The following table provide the details of standard floating-point types with storage sizes and value ranges and their precision −

Type	Storage size	Value range	Precision
float	4 byte	1.2E-38 to 3.4E+38	6 decimal places
double	8 byte	2.3E-308 to 1.7E+308	15 decimal places
long double	10 byte	3.4E-4932 to 1.1E+4932	19 decimal places

The header file float.h defines macros that allow you to use these values and other details about the binary representation of real numbers in your programs. The following example prints the storage space taken by a float type and its range values −

#include <stdio.h>

#include <float.h>

int main() {

   printf("Storage size for float : %d \n", sizeof(float));

   printf("Minimum float positive value: %E\n", FLT_MIN );

   printf("Maximum float positive value: %E\n", FLT_MAX );

   printf("Precision value: %d\n", FLT_DIG );

  

   return 0;

}

When you compile and execute the above program, it produces the following result on Linux −

Storage size for float : 4

Minimum float positive value: 1.175494E-38

Maximum float positive value: 3.402823E+38

Precision value: 6

The void Type

The void type specifies that no value is available. It is used in three kinds of situations −

S.N.	Types & Description
1	Function returns as void There are various functions in C which do not return any value or you can say they return void. A function with no return value has the return type as void. For example, void exit (int status);
2	Function arguments as void There are various functions in C which do not accept any parameter. A function with no parameter can accept a void. For example, int rand(void);
3	Pointers to void A pointer of type void * represents the address of an object, but not its type. For example, a memory allocation function void *malloc( size_t size ); returns a pointer to void which can be casted to any data type.