C - Constants & Variable declaration

Constants

A constant is a also identifier whose value can't be hanged during the program execution. In C language we can declare constant using const or #define macro. Constants are also called as Literals. C Constants is divided into 2 categories.

Numeric Constants
Character Constants

Numeric Constants

Numeric constants are again divided into 2 types.

Integer Constants
Real constants / Floating point Constants

Integer Constants

Integer constants accepts only integer data type values. They won't accept point values. They can be either 'positive or negative' constants are again divided into two categories.

Infix int const
Suffix int const

Infix int const

Infix integer constant indiates base of the value in which it has to be read.

Suffix int const

An integer literal(constant) can also have a suffix that is a combiantion of U and L, for unsigned and long, respectively.

Example:

123 /* By default it is consider has integer */
123U, 123u /* It means unsigned integer */
123l, 123L /*Long integer constant */
123ul /*Unsigned long integer constant */
078 /* Illegal: 8 is not octal digit */
032UU /* Illegal: cannot repeat a suffix */
85 /* Decimal */
0213 /* Octal */
0x4b /* hexadecimal */
30 /* Int */
30u /* unsigned int */
30l /* long */
30ul /* unsigned long */

Real Constants / Floating Point Constant

Real constants also known as floating point constants. These are having fractional part either positive or negative. These real constant again for 2 forms.

Decimal form: Decimal form it must contain decimal part.
Example:3.423, -8.964, 8, 93
Exponential form: Generally real or floating point constants are represented by using a format Mantissa
Mantissa: The part appearing before e, Mantissa is a real number expressed in decimal notation.
Exponent:Exponent is an integer number, it is positive or negative
Letter 'e': Letter 'e' separation the mantissa and exponent that can be written in either lowercase (or) uppercase.

⁴

^-2

⁵

^-1

Character Constants

Character constants are divided into 3 types:

Single Character Constants: A character constants which has been specified with in single quotes. This character maybe Letter(a, b, A, B, etc...) or maybe digit(1 to 9) or maybe symbol(%, #, <, ? etc...)
String Constants: A group of characters which are enclosed between double quotes are called as string constants.
ExampleHello or 5+10.
Back slash Character Constant
- There are some characters which have special meaning in C language.
- They should be preceded by backslash symbol to make use of special function of them.
- Giuen below is the list of special characters and their purpose.

S.No	Escape sequence	Character represented
1.	\a	ALert(bell, alarm)
2.	\b	Backspace
3.	\f	Form feed
4.	\n	new line
5.	\r	Carriage return
6.	\t	Horizontal tab
7.	\v	Vertical tab
8.	\'	Single Quotation mark
9.	\"	Double quotation mark
10.	\?	Question mark
11.	\\	Backslash
12.	\0	Null character

Variables

In programming, a variable is a container(storage area) to hold data. To indicate the storage area, each variable should be given a unique name (identifier). Variable names are just the symbolic representation of a memory location.

Example:int playerscore = 95;

Here, playerscore is a variable of int type. The int variable is assigned an integer value 95.

Rules for naming a variable:

A variable name can only have letters (both uppercase and lowercase letters), digits and underscore.
The first letter of a variable should be either a letter or an underscore. If you start with number it will not work as variable.
The variable name should not be a keyword
White space is not allowed.
There is no rule on how long a variable name(identifier) can be. However, you may run into problems in some compilers if the variable name si longer than 31 characters.
In C programming, we have to declare the variable before using it in the program.

How to declare a variable

The Variable declaration indicates that the operating system is going to reserve a piece of memory with that variable name.

Variable declaration

The syntax for variable declaration is as follows

type variable_name; (single variable declaration)
or
type variable_name, variable_name, variable_name; (Multiple variable declaration)

Syntax

int a,b,c;
int age;
char name;

Here a, b, c, age, name are variables. The int, char are the data types

Example program

#include<stdio.h>
int main() {
/* variable declaration */
int height, width;
height = 20;
width = 20;
printf("Value of height = %d \n value of width = %d", height, width);
return 0;
}

output

output is :

Value of height = 20
Value of width = 20