Data types in C programming

Data type is a system for defining various basic properties about the data stored in memory. Properties such as, type of data, range of data, bytes occupied, how these bytes are interpreted etc.

For example: int is a data type used to define integer type variables.
int a; here a is an integer type variable. It can store numbers from -2,147,483,648 to +2,147,483,647.

Data types in C is classified in three broad categories.

1. Primitive data type
2. Derived data type
3. User defined data type

Read more – List of all primitive and derived data types in C.

Primitive data type

C language supports four primitive types – char, int, float, void. Primitive types are also known as pre-defined or basic data types.

The size and range of a data type is machine dependent and may vary from compiler to compiler. C standard requires only the minimum size to be fulfilled by every compiler for each data type. For example, size of int type varies from compiler to compiler, but it must be at least 2 bytes on every compiler.

Character type char

Any single character value in C is represented using char. Size of char type is 1 byte and can store 128 characters.

Example to define char type variable –

char grade = 'A';

In above code grade is defined as a character type variable and can store any character.

Read more – How to declare character literal (value)?

Integer type int

In C programming int keyword is used to define a number type. Size of int is 2 or 4 bytes (compiler dependent) and can store values up to -32,768 to 32,767 or -2,147,483,648 to +2,147,483,647.

Example to define int type variable –

int roll = 24;

In above code roll is defined as an integer type variable and can store any number in int range.

Float type float

A real type value in C is defined with float or double keyword. float defines a single precision floating point number that can store 1.2E-38 to 3.4E+38. Whereas double defines a double precision floating point number that can store 2.3E-308 to 1.7E+308.

Number of significant digits after decimal point is known as its precision. Precision of float type is of 6 decimal places and double is of 15 decimal places.

Example to define float type variable –

float percentage = 95.67;
const float PI = 3.14159265359f;
double speed = 2.998e+8;

C considers floating point literal as double type. Add suffix f or F after floating point literal to specify type as float.

void type

As name suggests void internally does not store anything. void keyword is used to define a function return type or a generic pointer.

Example to define void pointer type –

void * ptr;

In the above code ptr is defined as a void pointer. We will learn about void types in later section of this programming tutorial series.

Derived data types

A derived data type is defined using combination of qualifiers along with the primitive data type. Derived types are created using basic data types with modified behaviour and property.

Data type Qualifiers

Qualifiers are optional add-on to the basic data types. They are used to alter the behaviour and property of basic data types yielding new type with new property and behaviour.

There are two types of data type qualifiers in C, size and sign qualifier. They are used along with the basic data types in any of the two given syntax.

[qualifier] <basic-data-type>

OR

<basic-data-type> [qualifier]

Standard syntax to use a qualifier

[sign-qualifier] [size-qualifier] <basic-data-type>

Example: unsigned short int

Note: Parts in the square brackets [] are optional and parts in angle bracket < > are mandatory.

Size qualifier

Size qualifier in C is used to alter size of a primitive data type. C supports two size qualifier, short and long.

Size qualifier is generally used with integer type. In addition, double type supports long qualifier.

Syntax to use size qualifier

[size-qualifier] <basic-data-type>

OR

<basic-data-type> [size-qualifier]

Example to use size qualifier

Rules regarding size qualifier as per ANSI C standard

• Size of short integer type short int is at least 2 bytes and must be less than or equal to the size of int
• The size of integer type int is at least 2 bytes and must be greater than or equal to the size of short.
• The size of long integer types long int is at least 4 bytes and must be greater than or equal to the size of int.
• The precision of long double must be greater than or equal to double. Precision of double must be greater or equal to the precision of float.

Note: short int may also abbreviated as short and long int as long. But, there is no abbreviation for long double.

The GCC C compiler supports one more derived integer type long long or long long int. Size of long long is 8 bytes and can store numbers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.

Must read –

• How to find size of a type using sizeof() operator?
• How to find range of a type in C?

Sign qualifier

Sign qualifier in C is used to specify signed nature of integer types. It specifies whether a variable can hold negative value or not.

Sign qualifiers are used with integer int and character char type.

C supports two sign qualifier, signed and unsigned. signed specifies a variable can hold both positive as well as negative integers. unsigned specifies a variable will only hold positive integers.

Example to use sign qualifier

signed short int
unsigned long
unsigned char

By default, integer and character types are signed in nature. Hence, using signed keyword is useless. However, a good programmer will use to explicitly specify signed nature of the variable.

User defined data type

Despite of several basic and derived type, C language supports feature to define our custom type based on our need. User defined type include array, pointer, structures, unions, enumeration types etc.

At this point with little knowledge of C programming, it is impossible to explain user defined types. I will cover them all in upcoming sections of this tutorial series.