Data Types and Constants in C-Chapter 1

jojo June 20, 2012 7 Comments

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.

C Data Types- C programming tutorial

Image Courtesy

  • 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.


Format Specifier


Date Range



1 byte

-128 to +127



2 bytes

0 to 255



4 bytes

-3.4e38 to +3.4e38



8 bytes

-1.7e38 to +1.7e38

long int


4 bytes

-231 to +231

unsigned int


2 bytes

0 to 65535

long double


16 bytes

-3.4e38 to +3.4e38

Unsigned char


1 byte

0 to 255


There are 4 types of constants in C.

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

C programming tutorialImage Courtesy

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




Hexa Decimal




Long Hexa Decimal


I or L

Unsigned Long Hexa Decimal


UI or UL

Long Octal


I or L

  • 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.

Example:   “Circuits Today123”

  • March 15, 2013

    sir when will you put info about derived data types and user defined data types

  • Elex Wood
    June 27, 2012

    Hey Can any will explain about “void” data type.

    • jojo
      June 27, 2012

      @Elex Wood

      “void” is usually used to declare functions that return nothing. I will explain more about “void” – when I write about the topic “Functions in C”.

  • June 22, 2012

    Thanks Jojo,
    It helped me a lot….GOOD JOB !!!

  • Luis
    June 21, 2012


    I just wanted to recommend maybe changing the font. On some parts of the text it’s hard to tell the difference between zero and the lower case letter ‘O’. Actually, on some parts you did type the letter ‘O’ and later on used the number zero to give the same example. Maybe someone with some experience may tell that there is a problem, but a beginner might get confused.

    Other than that, good post.

    • jojo
      June 21, 2012

      @Luis – Noticed the problem. It’s a problem of the font we use in website. Will correct that soon.

  • June 21, 2012

    Please visit the Site To learn Fundamentals of C Programming in Tamil. It is very useful for the Beginners.

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