C Identifiers

Identifier refers to name given to entities such as variables, functions, structures etc.

Identifier must be unique. They are created to give unique name to a entity to identify it during the execution of the program.

int money;
double accountBalance;

Here, money and accountBalance are identifiers.

C Keywords

Keywords are predefined, reserved words used in programming that have special meanings to the compiler. Keywords are part of the syntax and they cannot be used as an identifier. For example:

int money;

Here, int is a keyword that indicates 'money' is a variable of type integer.

C Programming Data Types

In C programming, variables or memory locations should be declared before it can be used. Similarly, a function also needs to be declared before use.

Data types simply refers to the type and size of data associated with variables and functions.

Data types in C

1. Fundamental Data Types
   • Integer types
   • Floating type
   • Character type
2. Derived Data Types
   • Arrays
   • Pointers
   • Structures
   • Enumeration

int - Integer data types

Integers are whole numbers that can have both positive and negative values but no decimal values. Example: 0, -5, 10

In C programming, keyword int is used for declaring integer variable. For example:

int id;

Here, id is a variable of type integer.

You can declare multiple variable at once in C programming. For example:

int id, age;

float - Floating types

Floating type variables can hold real numbers such as: 2.34, -9.382, 5.0 etc. You can declare a floating point variable in C by using either float or double keyword. For example:

float accountBalance;
double bookPrice;

Here, both accountBalance and bookPrice are floating type variables.

In C, floating values can be represented in exponential form as well. For example:

float normalizationFactor = 22.442e2;

Difference between float and double

The size of float (single precision float data type) is 4 bytes. And the size of double (double precision float data type) is 8 bytes. Floating point variables has a precision of 6 digits whereas the precision of double is 14 digits.

char - Character types

Keyword char is used for declaring character type variables. For example:

char test = 'h';

Here, test is a character variable. The value of test is 'h'.

The size of character variable is 1 byte.

Size qualifiers

Size qualifiers alters the size of a basic type. There are two size qualifiers, longand short. For example:

long double i;

The size of double is 8 bytes. However, when long keyword is used, that variable becomes 10 bytes.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.