C Programming Language - Data Types

In this tutorial you will learn about C language data types, Primary data type, Integer Type, Floating Point Types, Void Type, Character Type, Size and Range of Data Types on 16 bit machine, derived data type, Declaration of Variables, User defined type declaration, Declaration of Storage Class, auto, static, extern, register, Defining Symbolic Constants, Declaring Variable as Constant and Volatile Variable

A C language programmer has to tell the system before-hand, the type of numbers or characters he is using in his program. These are data types. There are many data types in C language. A C programmer has to use appropriate data type as per his requirement.

C language data types can be broadly classified as
Primary data type
Derived data type
User-defined data type

Primary data type

All C Compilers accept the following fundamental data types

The size and range of each data type is given in the table below

Integer Type :

Integers are whole numbers with a machine dependent range of values. A good programming language as to support the programmer by giving a control on a range of numbers and storage space. C has 3 classes of integer storage namely short int, int and long int. All of these data types have signed and unsigned forms. A short int requires half the space than normal integer values. Unsigned numbers are always positive and consume all the bits for the magnitude of the number. The long and unsigned integers are used to declare a longer range of values.

Floating Point Types :

Floating point number represents a real number with 6 digits precision. Floating point numbers are denoted by the keyword float. When the accuracy of the floating point number is insufficient, we can use the double to define the number. The double is same as float but with longer precision. To extend the precision further we can use long double which consumes 80 bits of memory space.

Void Type :

Using void data type, we can specify the type of a function. It is a good practice to avoid functions that does not return any values to the calling function.

Character Type :

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

Size and Range of Data Types on 16 bit machine.

Declaration of Variables

Every variable used in the program should be declared to the compiler. The declaration does two things.

1. Tells the compiler the variables name.
2. Specifies what type of data the variable will hold.

The general format of any declaration

datatype v1, v2, v3, ……….. vn;

Where v1, v2, v3 are variable names. Variables are separated by commas. A declaration statement must end with a semicolon.

Example:

Int sum;
Int number, salary;
Double average, mean;

User defined type declaration

In C language a user can define an identifier that represents an existing data type. The user defined datatype identifier can later be used to declare variables. The general syntax is

typedef type identifier;

here type represents existing data type and ‘identifier’ refers to the ‘row’ name given to the data type.

Example:

typedef int salary;
typedef float average;

Here salary symbolizes int and average symbolizes float. They can be later used to declare variables as follows:

Units dept1, dept2;
Average section1, section2;

Therefore dept1 and dept2 are indirectly declared as integer datatype and section1 and section2 are indirectly float data type.

The second type of user defined datatype is enumerated data type which is defined as follows.

Enum identifier {value1, value2 …. Value n};

The identifier is a user defined enumerated datatype which can be used to declare variables that have one of the values enclosed within the braces. After the definition we can declare variables to be of this ‘new’ type as below.

enum identifier V1, V2, V3, ……… Vn

The enumerated variables V1, V2, ….. Vn can have only one of the values value1, value2 ….. value n

Example:

enum day {Monday, Tuesday, …. Sunday};
enum day week_st, week end;
week_st = Monday;
week_end = Friday;
if(wk_st == Tuesday)
week_en = Saturday;

Declaration of Storage Class

Variables in C have not only the data type but also storage class that provides information about their location and visibility. The storage class divides the portion of the program within which the variables are recognized.

auto : It is a local variable known only to the function in which it is declared. Auto is the default storage class.

static : Local variable which exists and retains its value even after the control is transferred to the calling function.

extern : Global variable known to all functions in the file

register : Social variables which are stored in the register.

Defining Symbolic Constants

A symbolic constant value can be defined as a preprocessor statement and used in the program as any other constant value. The general form of a symbolic constant is

# define symbolic_name value of constant

Valid examples of constant definitions are :

# define marks 100
# define total 50
# define pi 3.14159

These values may appear anywhere in the program, but must come before it is referenced in the program.

It is a standard practice to place them at the beginning of the program.

Declaring Variable as Constant

The values of some variable may be required to remain constant through-out the program. We can do this by using the qualifier const at the time of initialization.

Example:

Const int class_size = 40;

The const data type qualifier tells the compiler that the value of the int variable class_size may not be modified in the program.

Volatile Variable

A volatile variable is the one whose values may be changed at any time by some external sources.

Example:

volatile int num;

The value of data may be altered by some external factor, even if it does not appear on the left hand side of the assignment statement. When we declare a variable as volatile the compiler will examine the value of the variable each time it is encountered to see if an external factor has changed the value.