Redireciton of input and output on linux shell..

Syntax:
linux-command redirection-symbol input/output-file-name

There are three basic redirection operators.

1. output (>)
   ex: $ ls > dirList.txt
   the output of the ls command will write in dirList.txt if the file is already present then it will be overwritten without any warning.
   
   
2. append (>>)
   To output Linux-commands result to the end of file (append). Note that if file exist , it will be opened and new information will be written to end of file, without losing previous information, And if file is not exist, then new file is created. For e.g. To send output of pstree command to already exist file give command
   ex: $ pstree >> processList.txt
   
   
3. input (<) To take input to Linux-command from file instead of key-board. If file does not exist then you have to give using key-board. ex: ./a.out < input.in
   

In Linux in C/CPP programming Language keyboard, screen etc are all treated as files. these files are:

File Name	Discriptor	Use	Example
Stdin	0	Standard Input	Keyboard
Stdout	1	Standard Output	Screen
Stderr	2	Standard Error	Screen

In linux every program has three files associated with it, (when we start our program these three files are automatically opened by the shell). The use of first two files (stdin and stdout) , are already seen by us. The last file stderr is used by our program to print error on screen. Error message can't be redirected, for example the Command $ rm file1.txt > getError.txt will not log the error(rm: cannot remove `file1.txt': No such file or directory) into the file getError.txt in case file1.txt does not present, since output is send to error device. But if still want to log the error, use the discriptor for example $ rm file1.txt 2>getError.txt

The logic behind Ethiopian multiplication.

This method of multiplication is also called Egyptian Multiplication (as believed it was developed in Egypt).

How it Works.

• write two no in the adjacent columns(smaller one in left side,


• In the left column recursively halve the number, discarding remainders,
  


• In the right column recursively double the number and write the result below, do this unlit left column shows 1,
  


• Test for the left column if it is odd then add corresponding no in the right column.
  
  

Example

A = 34;
B = 12;

B	A
12	34
6	68
3	136
1	272

_________________________________________
408
_________________________________________

12*34 = 136+272
= 34*4 + 34*8
= 34(4+8)
= 34(2²+2³)
= 34(12)

The main idea is that break the first no in the power of two and multiplication with 2 is easier. Then add to obtain result.

Useful links for me...

For job interview preparation.

1. http://web.iiit.ac.in/~avidullu/pdfs/crack_the_interview.pdf
   
2. http://www.allapplabs.com/interview_questions/java_interview_questions_7.htm
3. http://www.foddalo.com/

Puzzles

1. http://www.techinterview.org/
2. http://onepuzzleaday.blogspot.com/
   

Good blogs to hang with.

1. http://billthelizard.com/
2. http://hbfs.wordpress.com/2008/12/23/the-10-classes-of-algorithms-every-programmer-must-know-about/
3. http://www.jasonernst.com/category/wireless-networks/
   

Find existence and formula for any sequence.

1. http://www.research.att.com/~njas/sequences/

Tutorials

1. http://www.w3schools.com/
2. http://java.sun.com/docs/books/tutorial/java/nutsandbolts/index.html
3. http://www.idevelopment.info/data/Programming/java/PROGRAMMING_Java_Programming.shtml