C Qualifiers

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C Qualifiers

Qualifiers alters the meaning of base data types to yield a new data type.

Size qualifiers

Size qualifiers alters the size of a basic type. There are two size qualifiers, long and short. For example:
long double i;
The size of double is 8 bytes. However, when long keyword is used, that variable becomes 10 bytes.
Learn more about long keyword in C programming.
There is another keyword short which can be used if you previously know the value of a variable will always be a small number.

Sign qualifiers

Integers and floating point variables can hold both negative and positive values. However, if a variable needs to hold positive value only, unsigned data types are used. For example:
// unsigned variables cannot hold negative value 
unsigned int positiveInteger;
There is another qualifier signed which can hold both negative and positive only. However, it is not necessary to define variable signed since a variable is signed by default.
An integer variable of 4 bytes can hold data from -231 to 231-1. However, if the variable is defined as unsigned, it can hold data from 0 to 232-1.
It is important to note that, sign qualifiers can be applied to int and char types only.

Constant qualifiers

An identifier can be declared as a constant. To do so const keyword is used.
const int cost = 20;
The value of cost cannot be changed in the program.

Volatile qualifiers

A variable should be declared volatile whenever its value can be changed by some external sources outside the program. Keyword volatile is used for creating volatile variables.

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