C In Telugu About Long and Double Data Types part 6

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) == %dn”, sizeof(char));
printf(“sizeof(short) == %dn”, sizeof(short));
printf(“sizeof(int) == %dn”, sizeof(int));
printf(“sizeof(long) == %dn”, sizeof(long));
printf(“sizeof(float) == %dn”, sizeof(float));
printf(“sizeof(double) == %dn”, sizeof(double));
printf(“sizeof(long double) == %dn”, sizeof(long double));
printf(“sizeof(long long) == %dn”, 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.