Constants & Variables - C Language Tutorial

Definition
Constant is a number or a character representing a quantity, assumed to have fixed value.
Variable is a name given to memory location for storing a value and its value may vary during program execution.
Description

Constants

Constants are divided into three types : Integer, Real and Character. Each constant have some rules for building it and these rules must be followed, while writing the program.

Rules for Integer Constants
Must have at least one digit without any decimal point.
No commas or blank space are allowed.
It could be either positive or negative, For no sign specification it is assumed to be positive.
Eg: 93 , +541 , -383

Rules for Real constants
Must have at least one digit with decimal point.
No commas or blank space are allowed.
It could be either positive or negative, For no sign specification it is assumed to be positive.
Eg: 48.63 , +38.73 , -382.44

Rules for Character constants
Maximum character length must be 1.
It might be a single alphabet, a single digit or a single special symbol enclosed within single inverted commas.
Eg: 'a' , 'R', '4' , '='

Variables

Similar to constants, variables also have some rules for naming it.

Name can contain any combination of alphabets, digits or underscores, but first character must be alphabet or underscore.
No commas or blanks are allowed.
Keywords cannot be used as a variable name.
For declaring a variable you need to specify its name, data-type it can handle and a semi-colon at the end of declaration. Four basic data-types of variables are int, char, float and double.

Eg: int i;
char event;
float value;

Now you can initialize or assign values to these variables:

Eg: int i=0;
char event='a';
float value=834.22;

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