C Data type,Variables and Constants

In the C programming language, data types 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:

Types and Description  Basic Types:They are arithmetic types and consists of the two types: (a) integer types and (b) floating-point types.  Enumerated types:They are again arithmetic types and they are used to define variables that can only be assigned certain discrete integer values throughout the program.  The type void:The type specifier void indicates that no value is available.  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 to collectively as the aggregate types. The type of a function specifies the type of the function’s return value. We will see basic types in the following section, whereas, other types will be covered in the upcoming chapters.

Integer Types

Following table gives you details about standard integer types with its storage sizes and value ranges:   Storage sizeValue range  1 byte-128 to 127 or 0 to 255  1 byte0 to 255  1 byte-128 to 127  2 or 4 bytes-32,768 to 32,767 or -2,147,483,648 to 2,147,483,647  2 or 4 bytes0 to 65,535 or 0 to 4,294,967,295  2 bytes-32,768 to 32,767  2 bytes0 to 65,535  4 bytes-2,147,483,648 to 2,147,483,647  4 bytes0 to 4,294,967,295

unsigned charsigned charintunsigned intshortunsigned shortlongunsigned long


To get the exact size of a type or a variable on a particular platform, you can use the sizeofoperator. The expressions sizeof(type) yields the storage size of the object or type in bytes. Following 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

Following table gives you details about standard floating-point types with storage sizes and value ranges and their precision:   Storage sizeValue rangePrecision  4 byte1.2E-38 to 3.4E+386 decimal places  8 byte2.3E-308 to 1.7E+30815 decimal places  10 byte3.4E-4932 to 1.1E+493219 decimal places

doublelong double


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. Following example will print 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:   Types and Description  Function returns as voidThere are various functions in C which do not return 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);  Function arguments as voidThere are various functions in C which do not accept any parameter. A function with no parameter can accept as a void. For example, int rand(void);  Pointers to voidA 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.



The void type may not be understood to you at this point, so let us proceed and we will cover these concepts in the upcoming chapters.

C – Variables

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C has a specific type, which determines the size and layout of the variable’s memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.   The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because C is case-sensitive. Based on the basic types explained in previous chapter, there will be the following basic variable types:   Description  Typically a single octet(one byte). This is an integer type.  The most natural size of integer for the machine.  A single-precision floating point value.  A double-precision floating point value.  Represents the absence of type.



C programming language also allows to define various other types of variables, which we will cover in subsequent chapters like Enumeration, Pointer, Array, Structure, Union, etc. For this chapter, let us study only basic variable types.

Variable Definition in C:

A variable definition means to tell the compiler where and how much to create the storage for the variable. A variable definition specifies a data type and contains a list of one or more variables of that type as follows:

type variable_list;

Here, type must be a valid C data type including char, w_char, int, float, double, bool or any user-defined object, etc., and variable_list may consist of one or more identifier names separated by commas. Some valid declarations are shown here:

int    i, j, k;
char   c, ch;
float  f, salary;
double d;

The line int i, j, k; both declares and defines the variables i, j and k; which instructs the compiler to create variables named i, j and k of type int.   Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as follows:

type variable_name = value;

Some examples are:

extern int d = 3, f = 5;    // declaration of d and f. 
int d = 3, f = 5;           // definition and initializing d and f. 
byte z = 22;                // definition and initializes z. 
char x = 'x';               // the variable x has the value 'x'.

For definition without an initializer: variables with static storage duration are implicitly initialized with NULL (all bytes have the value 0); the initial value of all other variables is undefined.

Variable Declaration in C:

A variable declaration provides assurance to the compiler that there is one variable existing with the given type and name so that compiler proceed for further compilation without needing complete detail about the variable. A variable declaration has its meaning at the time of compilation only, compiler needs actual variable declaration at the time of linking of the program.   A variable declaration is useful when you are using multiple files and you define your variable in one of the files which will be available at the time of linking of the program. You will use extern keyword to declare a variable at any place. Though you can declare a variable multiple times in your C program but it can be defined only once in a file, a function or a block of code.


Try following example, where variables have been declared at the top, but they have been defined and initialized inside the main function:

#include <stdio.h>

// Variable declaration:
extern int a, b;
extern int c;
extern float f;

int main ()
  /* variable definition: */
  int a, b;
  int c;
  float f;
  /* actual initialization */
  a = 10;
  b = 20;
  c = a + b;
  printf("value of c : %d \n", c);

  f = 70.0/3.0;
  printf("value of f : %f \n", f);
  return 0;

When the above code is compiled and executed, it produces the following result:

value of c : 30
value of f : 23.333334

Same concept applies on function declaration where you provide a function name at the time of its declaration and its actual definition can be given anywhere else. For example:

// function declaration
int func();

int main()
    // function call
    int i = func();

// function definition
int func()
    return 0;


Lvalues and Rvalues in C:

There are two kinds of expressions in C:


      1. lvalue : Expressions that refer to a memory location is called “lvalue” expression. An lvalue may appear as either the left-hand or right-hand side of an assignment.



    • rvalue : The term rvalue refers to a data value that is stored at some address in memory. An rvalue is an expression that cannot have a value assigned to it which means an rvalue may appear on the right- but not left-hand side of an assignment.


Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a valid statement:

int g = 20;

But following is not a valid statement and would generate compile-time error:   10 = 20;


The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals.   Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well.   The constants are treated just like regular variables except that their values cannot be modified after their definition.

Integer literals

An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal.   An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.   Here are some examples of integer literals:

212         /* Legal */
215u        /* Legal */
0xFeeL      /* Legal */
078         /* Illegal: 8 is not an octal digit */
032UU       /* Illegal: cannot repeat a suffix */

Following are other examples of various type of Integer literals:

85         /* decimal */
0213       /* octal */
0x4b       /* hexadecimal */
30         /* int */
30u        /* unsigned int */
30l        /* long */
30ul       /* unsigned long */


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.   While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form, you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.   Here are some examples of floating-point literals:

3.14159       /* Legal */
314159E-5L    /* Legal */
510E          /* Illegal: incomplete exponent */
210f          /* Illegal: no decimal or exponent */
.e55          /* Illegal: missing integer or fraction */


Character constants

Character literals are enclosed in single quotes, e.g., ‘x’ and can be stored in a simple variable of char type.   A character literal can be a plain character (e.g., ‘x’), an escape sequence (e.g., ‘\t’), or a universal character (e.g., ‘\u02C0’).   There are certain characters in C when they are preceded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here, you have a list of some of such escape sequence codes:   Meaning  \ character  ‘ character  ” character  ? character  Alert or bell  Backspace  Form feed  Newline  Carriage return  Horizontal tab  Vertical tab  Octal number of one to three digits  Hexadecimal number of one or more digits

\’\”\?\a\b\f\n\r\t\v\ooo\xhh . . .

Escape sequence

Following is the example to show few escape sequence characters:

#include <stdio.h>

int main()

   return 0;

When the above code is compiled and executed, it produces the following result:

Hello   World


String literals

String literals or constants are enclosed in double quotes “”. A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters.   You can break a long line into multiple lines using string literals and separating them using whitespaces.   Here are some examples of string literals. All the three forms are identical strings.

"hello, dear"

"hello, \


"hello, " "d" "ear"


Defining Constants

There are two simple ways in C to define constants:


      1. Using #define preprocessor.



    • Using const keyword.



The #define Preprocessor

Following is the form to use #define preprocessor to define a constant:

#define identifier value

Following example explains it in detail:

#include <stdio.h>

#define LENGTH 10   
#define WIDTH  5
#define NEWLINE '\n'

int main()

   int area;  
   area = LENGTH * WIDTH;
   printf("value of area : %d", area);
   printf("%c", NEWLINE);

   return 0;

When the above code is compiled and executed, it produces the following result:

value of area : 50


The const Keyword

You can use const prefix to declare constants with a specific type as follows:

const type variable = value;

Following example explains it in detail:

#include <stdio.h>

int main()
   const int  LENGTH = 10;
   const int  WIDTH  = 5;
   const char NEWLINE = '\n';
   int area;  
   area = LENGTH * WIDTH;
   printf("value of area : %d", area);
   printf("%c", NEWLINE);

   return 0;

When the above code is compiled and executed, it produces the following result:

value of area : 50

Note that it is a good programming practice to define constants in CAPITALS.