Data Types and Constants in C-Chapter 1

To use any language in communication (to write/to speak), we need to understand it’s grammar first.  In the case of a programming language like C, the scenario is same as in the case of a communication language. We need to understand the grammar of C programming language first. So here begins:-

In this article we explain Data Types and Constants

The basic grammar of C can be explained through:-

• Data Types
• Constants
• Variables and Keywords
• Operators and Operands
• Control structures (branching and looping)
• Functions
• Arrays
• Strings
• Pointers
• Structures
• Files

Data Types

There are 4 data types in C language. They are:-

• int – This data type is used to define an integer number (-….-3,-2,-1,0,1,2,3….). A single integer occupies 2 bytes.
• char – Used to define characters. A single character occupy 1 byte.
• float – Used to define floating point numbers (single precision). Occupies 4 bytes.
• double – Used for double precision floating point numbers(double precision). Occupies 8 bytes.

Note:- Single precision and Double precision basically differs in the number of digits represented after the decimal point. Double precision number will represent more digits after the decimal point than a single precision number. Example:- Single precision – 32.75   and double precision –  32.7543

Data Types can also be classified as shown in the image below – Primitive, Derived and User Defined.

• Primitive data types are the first form – the basic data types (int,char,float,double).
• Derived data types are a derivative of primitive data types known as arrays, pointer and function.
• User defined data types are those data types which are defined by the user/programmer himself.

Note: We will learn about Derived and user defined data types in coming chapters.

Data Type Qualifiers

Each of these data type has got qualifiers. The purpose of a qualifier is to manipulate the range of a particular data type or its size. The 4 qualifiers in C are long,short,signed and unsigned.First two long and short are called size qualifiers and the other two signed and unsigned are called sign qualifiers.

Example: int – when declared normally is of 2 bytes. If it is declared as unsigned int – then its range is from 0 to 65535. In other case, if it is declared as signed int – then its range is from (-32767 to 32768). In the case of signed int, one bit (MSB) is used to store the sign of the integer +/-. This basically means the programmer will not be able to display/store a number higher than 65535 using unsigned int. Similarly it is not possible to manipulate a number beyond -32767 or +327678 using signed int.

The qualifiers long and short are used to increase storage size of the data type.

Example: Integer data type int is normally 2 byte. If you declare it as long int – then its size will increase from 2 bytes to 4 bytes. Similarly if you declare it as short int – its size will reduce from 2 bytes to 1 byte. 

The table below describes all data types and the most commonly used qualifier combinations – with its size,range and format specifier. Note: You will learn more about the use of format specifiers in coming chapters.

Keyword	Format Specifier	Size	Date Range
char	%c	1 byte	-128 to +127
int	%d	2 bytes	0 to 255
float	%f	4 bytes	-3.4e38 to +3.4e38
double	%lf	8 bytes	-1.7e38 to +1.7e38
long int	%ld	4 bytes	-231 to +231
unsigned int	%u	2 bytes	0 to 65535
long double	%Lf	16 bytes	-3.4e38 to +3.4e38
Unsigned char	%c	1 byte	0 to 255

Constants

There are 4 types of constants in C.

• Integer constants
• Character constants
• Real/Floating point constants
• String constants

By definition, a constant is a quantity that does not change throughout the execution of a program.

Integer Constants

An integer constant is an integer quantity which contains a sequence of digits.It should not have a decimal point. Blanks and commas are not allowed within an integer constant.An integer constant can be either +ve or -ve. The constant must lie within the range of the declared data type (including qualifiers long,short etc.).

Example of valid integer constants:- 976    8987   5   -25  etc.

Example of invalid integer constants:-  78.43   7-8   89,76  etc.

An integer constant can be either Decimal, Hexa Decimal or Octal. See the table below to understand how these 3 different constants are defined in C.

Integer Type	Prefix	Suffix	Example
Hexa Decimal	Ox		OxA7B
Octal	O		O54
Long Hexa Decimal	Ox	I or L	OxA7BL
Unsigned Long Hexa Decimal	Ox	UI or UL	OxA7FUI
Long Octal	O	I or L	O54L

• A decimal constant can contain any combination of integers from 0 through 9. Ex: 189      0      75       87
• A hexa decimal constant should begin with 0X or 0x. Ex: 0x65F  or 0X7A
• An octal constant should begin with digit 0. It can take any digits from 0 through 7.

Note:- There is no binary integer constant in C by default. This means, you cant give a binary number directly to program by writing sth like:- 0b11001011 – which is meaningless and result in an error. How ever, programmer can add a preprocessor (which we will learn later) to accept binary numbers in a program.

Floating Point Constants

They are also known as real constants. A real constant contains a decimal point or an exponent. It can be either +ve or -ve. Commas and blank space are not allowed within a real constant.


Examples:– 254.175,      -16.47      -0.5e-7     +4.1e8

Character Constant

A character constant is a character which is enclosed in single quotes. A character constant is of size 1byte and can contain only 1 character. A character can be an alphabet like a,b,A,C etc or a special character like &,^, $, #,@ etc or a single digit from 0 through 9. It can also be an escape sequence character like space ‘ ‘ or a null character ‘\o’  or  a new line ‘\n’  etc.


Example: ‘A’       ‘a’     ‘ b’      ‘8’     ‘#’  etc.


Each character has a corresponding ASCII value. ASCII value is the numeric code of a particular character and is stored inside the machine’s character set.


Note:- It is good that you read more about ASCII. There are basically two types of ASCII characters known as control characters and printable characters. Control characters are usually used to control a device using the program or to manipulate some logic inside a program. Control characters are not usually printed to an output device. Printable characters are usually printed to a display device or a printer.

String Constants

1. A string constant is a collection of characters enclosed in double quotations “”
2. It may contain alphabets, digits, special characters and blank space.
3.