C language supports rich set of data types. Storage representations and machine instructions to handle constants differ from machine to machine. The variety of data types available allow the programmer to select appropriate to the needs to the applications as well ANSI C supports four types of data types:

  1. primary data types
  2. User defined data types
  3. Derived data types
  4. Empty dataset.

Primary data types:
An atomic data is a fundamental unit of information which cannot be broken down to constituent parts .All C compilers support four fundamental data types . The type of data type supported in language dictates the type of values which can be processed by the language.
The four main data types are:

  1. int (it holds an integer value)
  2. float (floating point)
  3. char (character)
  4. double (double precision floating point values)

Integers are whole numbers with a range of values supported by the machine. Generally the integer occupy one word of storage and since the word sizes of machines vary (typically 16 or 32 bits) the size of the integer that can be stored depends on the computer .However we have two types here

  1. signed
  2. unsigned

A signed integer uses one bit for the sign and 15 bits for the magnitude of the given number whereas in the case of unsigned integer it only uses all the 16 bits for the magnitude of the number ignoring the sign.
C has three classes of integer storage, namely short int, int, long int in both signed and unsigned cases
Usually the range of the unsigned numbers will be from 0 to 65535
Short int represents fairly a small integer values and requires half the amount of storage as a regular int number uses. We declare long and unsigned values to increase the range of number values. The use of qualifier “signed” on integers is optional because by default declaration assumes as a signed number.


Floating point or real numbers are stored in 32 bits ,with 6 digits of precision .floating point numbers are defined by the key word “float “. When the accuracy provided by a float number is not sufficient then , the double can be used to define a number .A double data type uses 64 bits with a precision of 14 digits. These are known as double precision numbers.
Double and float represent same data type but double differs from float in precision of digits.

Character types:

A single character can be defined as character data type .Characters are usually stored in 8 bits of internal storage. The qualifier signed or unsigned may be explicitly applied to char. While unsigned chars have values between 0 to 255.signed chars have values from -128 to 127.


The data types that are derived from primary data types .These are derived from one or more simple data types. Data types such as arrays, structures, unions, pointers come under category.


In addition to these data types there exists some data types that user can define in a program for simpler use ,such data types are called user defined data types .
There are two different types of user defined data types. They are

  1. typedef
  2. enum

C supports a feature called “type definition” that allows user to define an identifier that would represent an existing data type. The user defined data type identifier can later be used to declare variables. It takes the general form
typedef type identifier;
Where type refers to the existing data type and identifier refers to the “new “name given to the data type. The existing data type may belong to any class of type, including the user defined ones.
We should note that the new type is only new in name but not in data type .The typedef cannot create a new type.
Examples: typedef int units;
typedef float marks;
Here, the units represent the int and the marks represent the float .They can be later be used to declare variables as
units batch1, batch2;
marks name1 [15], name2[15];
Here the unit symbolizes int and marks refer to float .batch1 and batch2 are declared as int variable and name1 [15], name2 [15] are declared as 15 floating point array values. The main advantage of typedef is that we can create meaningful data type names for increasing the readability of the program .
ENUM: Enum is another user defined data type called enumerated data type .It is defined as follows:
enum identifier {value1, value2, value3, ……………, value n};
Where the identifier is a user defined enumerated data type which can be used to declare variables that can have one of the values enclosed within the braces (known as enumeration constants). After this definition, we can declare the variables to be of this ‘new’ type as below:
enum identifier v1,v2,v3………., vn;
enum day {Monday, Tuesday, Wednesday, Friday, Saturday, Sunday };
enum day week_st , week_end;
if (week_st==Tuesday)
The C compiler automatically assigns integer digits beginning with 0 to all the enumeration constants. That is, the enumeration constant value1 is assigned 0,value2 is assigned 1 and so on. However the automatic assignments can be over ridden by assigning values explicitly to the enumeration constants.
The declaration and definition of enumerated variables can be combined in one statement
enum day{Monday, Tuesday,…….., Sunday}week_st, week_end;

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