2007-08-29 |  RatheeshTR  | Viewed: 401  |    1

Variable Names:

There are some restrictions on the names of variables and symbolic constants. names are made up of letters and digits the first character must be a letter. The underscore "_" counts as a letter it is sometimes useful for improving the readability of long varaible names.

Examples of legal variable names include

x         	 result         	outfile          bestyet
x1        	x2             		 out_file        best_yet
power      impetus             gamma      hi_score

Fundamental data types:

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.

Name	Description	Size*	Range*
char	Character or small integer.	1byte	signed: -128 to 127 unsigned: 0 to 255
short int (short)	Short Integer.	2bytes	signed: -32768 to 32767 unsigned: 0 to 65535
int	Integer.	4bytes	signed: -2147483648 to 2147483647 unsigned: 0 to 4294967295
long int (long)	Long integer.	4bytes	signed: -2147483648 to 2147483647 unsigned: 0 to 4294967295
bool	Boolean value. It can take one of two values: true or false.	1byte	true or false
float	Floating point number.	4bytes	3.4e +/- 38 (7 digits)
double	Double precision floating point number.	8bytes	1.7e +/- 308 (15 digits)
long double	Long double precision floating point number.	8bytes	font size="2" face="Arial">1.7e +/- 308 (15 digits)
wchar_t	Wide character.	2bytes	1 wide character

The word int can be omitted in such declarations and typically is
The intent is that short and long should provide different lengths of integers where practical; int will normally be the natural size for a particular
machine. short is often 16 bits, long 32 bits, and int either 16 or 32 bits. Each compiler is free to choose appro
short int samp;
long int count;

The word int can be omitted in such declarations and typically is
The intent is that short and long should provide different lengths of integers where practical; int will normally be the natural size for a particular
machine. short is often 16 bits, long 32 bits, and int either 16 or 32 bits. Each compiler is free to choose appropriate sizes for its either 16 or 32 bits

Some data type Samples:

int - data type:

int Count;
Count = 5;

float - data type:

float avg;
avg = 5.6;

double - data type:

double Atoms;
Atoms = 2500000;

char - data type

char Letter;
Letter = 'x';

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.

Qualifiers:

* const
* volatile

The const qualifier is used to tell C that the variable value can not change after initialisation.

eg,
const float pi=3.14159;

pi cannot be changed at a later time within the program.
Another way to define constants is with the #define preprocessor

eg,

#define pi 3.14159;

sample program:

#include

int main ()
{
// declaring variables:
int a, b;
int result;

// process:
a = 5;
b = 2;
a = a + 1;
result = a - b;

// print out the result:
printf("%d", result);

// terminate the program:
return 0;
}

To cast, casting:

If you want to change the datatype of a variable you have to use a technic called cast.
For example if want to change an int to a float you could use the following syntax:

var2 = (float)var1;

#include

int main()
{
int var1;
float var2;

var2 = (float)var1;
}