Data Types in C :Langauge

Data Types in C :

"Data type can be defined as the type of data of variable or constant store."
When we use a variable in a program then we have to mention the type of data. This can be handled using data type in C.
Followings are the most commonly used data types in C.

Keyword	Format Specifier	Size	Data Range
char	%c	1 Byte	-128 to +127
unsigned char	<-- -- >	8 Bytes	0 to 255
int	%d	2 Bytes	-32768 to +32767
long int	%ld	4 Bytes	-231 to +231
unsigned int	%u	2 Bytes	0 to 65535
float	%f	4 Bytes	-3.4e38 to +3.4e38
double	%lf	8 Bytes	-1.7e38 to +1.7e38
long double	%Lf	12-16 Bytes	-3.4e38 to +3.4e38

* QUALIFIER :
When qualifier is applied to the data type then it changes its size or its size.
Size qualifiers : short, long
Sign qualifiers : signed, unsigned


* ENUM DATA TYPE :
This is an user defined data type having finite set of enumeration constants. The keyword 'enum' is used to create enumerated data type.
Syntax:
enum [data_type] {const1, const2, ...., const n};


Example:
enum mca(software, web, seo);


* TYPEDEF :
It is used to create new data type. But it is commonly used to change existing data type with another name.
Syntax:
typedef [data_type] synonym;


OR


typedef [data_type] new_data_type;


Example:
typedef int integer;
integer rno;




C has a concept of 'data types' which are used to define a variable before its use. The definition of a variable will assign storage for the variable and define the type of data that will be held in the location.
The value of a variable can be changed any time.
C has the following basic built-in datatypes.

• int
• float
• double
• char

Please note that there is not a boolean data type. C does not have the traditional view about logical comparison, but thats another story.

int - data type
int is used to define integer numbers.
    {
        int Count;
        Count = 5;
    }

float - data type
float is used to define floating point numbers.

    {
        float Miles;
        Miles = 5.6;
    }


double - data type
double is used to define BIG floating point numbers. It reserves twice the storage for the number. On PCs this is likely to be 8 bytes.

    {
        double Atoms;
        Atoms = 2500000;
    }


char - data type
char defines characters.

    {
        char Letter;
        Letter = 'x';
    }


Modifiers
The data types explained above have the following modifiers.
• short
• long
• signed
• unsigned


The modifiers define the amount of storage allocated to the variable. The amount of storage allocated is not cast in stone. ANSI has the following rules:

        short int <=    int <= long int
            float <= double <= long double

What this means is that a 'short int' should assign less than or the same amount of storage as an 'int' and the 'int' should be less or the same bytes than a 'long int'. What this means in the real world is:
 

Type Bytes             Range ---------------------------------------------------------------------

short int  2          -32,768 -> +32,767          (32kb)    unsigned short int  2                0 -> +65,535          (64Kb)          unsigned int  4                0 -> +4,294,967,295   ( 4Gb)                   int  4   -2,147,483,648 -> +2,147,483,647   ( 2Gb)              long int  4   -2,147,483,648 -> +2,147,483,647   ( 2Gb)           signed char  1             -128 -> +127         unsigned char  1                0 -> +255                 float  4                double  8            long double 12

These figures only apply to todays generation of PCs. Mainframes and midrange machines could use different figures, but would still comply with the rule above.
You can find out how much storage is allocated to a data type by using the sizeof operator discussed in Operator Types Session.
Here is an example to check size of memory taken by various datatypes.

int main() {   printf("sizeof(char) == %d\n", sizeof(char));   printf("sizeof(short) == %d\n", sizeof(short));   printf("sizeof(int) == %d\n", sizeof(int));   printf("sizeof(long) == %d\n", sizeof(long));   printf("sizeof(float) == %d\n", sizeof(float));   printf("sizeof(double) == %d\n", sizeof(double));   printf("sizeof(long double) == %d\n", sizeof(long double));   printf("sizeof(long long) == %d\n", sizeof(long long));   return 0; }

Qualifiers

A type qualifier is used to refine the declaration of a variable, a function, and parameters, by specifying whether:
• The value of a variable can be changed.
• The value of a variable must always be read from memory rather than from a register

Standard C language recognizes the following two qualifiers:
• const
• volatile

The const qualifier is used to tell C that the variable value can not change after initialisation.
const float pi=3.14159;
Now pi cannot be changed at a later time within the program.
Another way to define constants is with the #define preprocessor which has the advantage that it does not use any storage
The volatile qualifier declares a data type that can have its value changed in ways outside the control or detection of the compiler (such as a variable updated by the system clock or by another program). This prevents the compiler from optimizing code referring to the object by storing the object's value in a register and re-reading it from there, rather than from memory, where it may have changed. You will use this qualifier once you will become expert in "C". So for now just proceed.


What are Arrays:
We have seen all baisc data types. In C language it is possible to make arrays whose elements are basic types. Thus we can make an array of 10 integers with the declaration.
int x[10];

The square brackets mean subscripting; parentheses are used only for function references. Array indexes begin at zero, so the elements of x are:
Thus Array are special type of variables which can be used to store multiple values of same data type. Those values are stored and accessed using subscript or index.
Arrays occupy consecutive memory slots in the computer's memory.

x[0], x[1], x[2], ..., x[9]

If an array has n elements, the largest subscript is n-1.
Multiple-dimension arrays are provided. The declaration and use look like:

      int name[10] [20];
      n = name[i+j] [1] + name[k] [2];

Subscripts can be arbitrary integer expressions. Multi-dimension arrays are stored by row so the rightmost subscript varies fastest. In above example name has 10 rows and 20 columns.
Same way, arrays can be defined for any data type. Text is usually kept as an array of characters. By convention in C, the last character in a character array should be a `\0' because most programs that manipulate character arrays expect it. For example, printf uses the `\0' to detect the end of a character array when printing it out with a `%s'.

Here is a program which reads a line, stores it in a buffer, and prints its length (excluding the newline at the end).

       main( ) {
               int n, c;
               char line[100];
               n = 0;
               while( (c=getchar( )) != '\n' ) {
                       if( n < 100 )
                               line[n] = c;
                       n++;
               }
               printf("length = %d\n", n);
       }


Array Initialization
• As with other declarations, array declarations can include an optional initialization
• Scalar variables are initialized with a single value
• Arrays are initialized with a list of values
• The list is enclosed in curly braces
int array [8] = {2, 4, 6, 8, 10, 12, 14, 16};

The number of initializers cannot be more than the number of elements in the array but it can be less in which case, the remaining elements are initialized to 0.if you like, the array size can be inferred from the number of initializers by leaving the square brackets empty so these are identical declarations:

int array1 [8] = {2, 4, 6, 8, 10, 12, 14, 16};
int array2 [] = {2, 4, 6, 8, 10, 12, 14, 16};
An array of characters ie string can be initialized as follows:
char string[10] = "Hello";