What is Endianness Little Endian and Big Endian byte order in C

What is endianness ?
Endianness is the way bytes are stored in computer's memory address.
In a 32 bits machine an integer is 32 bits ie 4 bytes as bits are divided in group of 8 bits.so
For example,
suppose we have a 32 bit quantity, written as ox90AB12CD16, which is in hexadecimal.
So, the 4 bytes are: 90, AB, 12, CD where each byte requires 2 hex digits.

There are two ways to store this in memory(as memory is considered as array of bytes).

1. Big Endian
In big endian, the most significant byte is stored in the smallest address. Here's how it would look:

Address  Value    
1000     90                    you may also like linked list questions asked in recent interviews 2014
1001     AB
1002     12
1003     CD
ie 90, AB, 12, CD
If it is an integer say 1 then in a big endian machine it will be stored as 00  00  00  01

2. Little Endian
In little endian, you store the least significant byte in the smallest address. Here's how it would look:

Address  Value
1000     CD                      You may also like user defined string functions asked in recent walkins 2014
1001     12
1002     AB
1003     90
i.e. CD 12 AB 90
If it is an integer say 1 then in a little endian machine it will be stored as 01  00  00  00

How to find the endianness of a machine?
Below code tells how to know the Endianness of a machine.
#include<stdio.h>
int main()
{

   unsigned int i = 1;

   char *c = (char*)&i;/*a character pointer c is pointing to an integer i*/

   if (*c)    /*Since size of character is 1 byte when the character pointer is de-referenced it will contain only first byte of integer.*/

    printf("Your machine is Little endian.\n");//01 00 00 00 because 01 means 1 and true

   

else

       printf("It is a Big endian Machine.\n");//00 00 00 01

   

   return 0;

}

Explanation:
In the above program,
a character pointer c is pointing to an integer i.
Since size of character is 1 byte when the character pointer is de-referenced it will contain only first byte of integer.
So,
if machine is little endian then *c will be 1 (because last_byte/list_signifant_byte  is stored first/in lowes memory address in little endian. ) 00 00 00 01
and
if machine is big endian then *c will be 0 (because fisrt byte is stored firs) 01 00 00 00

Output on a ubuntu terminal is "little endian machine". means 1 was stored as 01 00 00 00
so if you print ox01234567 in little endian then it is stored as 67 45 23 01

Examples:
Generally Intel based processors are little endians. ARM processors were little endians.
 Current generation ARM processors are bi-endian.
Motorola 68K processors are big endians. PowerPC (by Motorola) and SPARK (by Sun)

thesse are most frequently asked interview questions in walk-ins and current interviews regarding eandian ness of a mchine.
Why endianness is used or why the ordering of bytes matter?
endian ness concept is must for network programs like socket programs as it is used by various types of machine and the program should work as desired in all the machines irrespective of it is a little or big endian machine.

There is also a concept of bi-endian hardware.