Programming Tutorial

JSON to POJO class creation in Android studio - Kotlin/Java

2020-12-07T21:03:00.004-08:00

Useful Linux Commands

2018-12-24T12:17:00.002-08:00

1. find command used to searches files or directories in entire file system or in current directory

find . -name *.java //searches all files with extension .java in current directory

find / -name Sample -type f // "-type f" option used to return only files

find / -name Sample -type d // "-type d" option used to return only directories

find /usr -name "Sample*" -type f // searches through the /usr directory for all files that begin with the letters Sample, followed by anything else

find . -type d -name build // to find all directories named build under the current directory

find . -type f -name "Foo*" -exec rm {} \; // find all files in the current directory that begin with the letters 'Foo' and delete them

find . -iname foo // Search for all files and directories named foo, FOO, or any other combination of uppercase and lowercase characters in the current directory

find . -mtime -7 // To find all files and directories that have been modified in the last seven days
find . -mtime -7 -type f // To find all files that have been modified in the last seven days
find . -mtime -7 -type d // To find all directories that have been modified in the last seven days
find /opt /usr /var -name sample.sh -type f // Searches "samples.sh" file in multiple directories

2. locate command is used for search files and directories

locate tomcat.sh // search the entire file system for 'tomcat.sh' (uses the locate database)
locate -i spring.jar // case-insensitive search

3. grep command is used for search strings

grep 'joe' * // Search for string in multiple files
grep -i score sample.txt // case-insensitive file searching
grep -n we sample.txt // To show the line numbers of the files that match your grep command, just add the -n option
grep -inR "text" . // case-insensitive file searching in current directory
grep 'fred' /etc/passwd // search for lines containing 'fred' in /etc/passwd
grep fred /etc/passwd // quotes usually not when you don't use regex patterns
grep -B5 "the living" sample.txt //show all matches, and five lines before each match
grep -A10 "the living" sample.txt // show all matches, and ten lines after each match
grep -B5 -A5 "the living" sample.txt //five lines before and ten lines after
grep -n we sample.txt // show line numbers as well as the matching lines
grep '^fred' /etc/passwd //find 'fred', but only at the start of a line
grep '[FG]oo' * // find Foo or Goo in all files in the current dirgrep '[0-9][0-9][0-9]' * // find all lines in all files in the current dir with three numbers in a row
egrep 'apple|banana|orange' * // search for multiple patterns, all files in current dir
egrep -i 'apple|banana|orange' * // same thing, case-insensitive
egrep 'score|nation|liberty|equal' sample.txt // all lines matching multiple patterns
egrep 'score|nation|liberty|equal' gettysburg-address.txt // This Unix egrep command searches the file named gettysburg-address.txt for the four strings shown (score, nation, liberty, and equal). It returns any lines from the file that contain any of those words.

4. cat command is used to view text files

cat -n myfile.txt // Showing line numbers
cat /etc/passwd // to view the contents of the /etc/passwd file on your Unix/Linux system
cat sample.txt // display the content of the file

5. wc command is used for count

$ wc /etc/passwd // to count the number of lines, words, and characters in a file
65 185 3667 /etc/passwd

$ wc -l /etc/passwd // If you just want to know the number of lines in a file just add the -l argument
65 /etc/passwd

$ wc -w MyStory.txt // if you want to know the number of words in a file, add the -w argument, like this
185 MyStory.txt

ps -e | wc -l // shows the number of processes currently running on your Linux system

6. rm command is used for removing files or directories

rm oldfile.txt // to remove one file
rm file1 file2 file3 // to delete multiple Linux files at one time
rm -i files file2 file3 // The -i stands for "inquire", so when you use this option the rm command prompts you with a yes/no prompt before actually deletingrm -r OldDirectory // To delete Linux directories with the rm command, you have to specify the -r optionrm -r Directory1 Directory2 Directory3 // delete multiple directories at one timerm *.html // to delete all HTML files in the current directoryrm index* // where I'm deleting all files in the current directory that begin with the string "index"

7. mv command to rename or move Linux files and directories

mv Chapter1 Chapter1.old
mv MyStuff /tmp // if you have a directory named MyStuff, you can move it to the /tmp directory
mv file1 file2 file3 /tmp // where three files are moved to the /tmp directory
mv file1 .. // if you want to move it up one level in the directory hierarchy

8. pwd to get current directory path

$ pwd
/home/techchai/

9. mkdir command is used for creating directories

mkdir tmp // creates a new directory named tmp in your current directory
mkdir memos letters e-mail // create multiple directories at one time
mkdir -p /home/joe/customer/acme/foo/bar // to create several sub directories at one time

10. ls command is used to list files and directories

ls -al // show all the files in cyrrent directory

11. tar command is used to create tar files

tar cvf MyProject.20090816.tar MyProject // tar command is to create an archive of a subdirectory.

c means “create archive.”
v means “verbose,” which tells tar to print all the filenames as they are added to the archive.
f tells tar that the name of the archive appears next (right after these options).

tar tvf my-archive.tar // List the contents of a tar archivetar tzvf my-archive.tgz //To list all the files in a compressed archive, add the z flag
tar xvf my-archive.tar // Extracting a tar archive
tar xzvf my-archive.tar.gz // For compressed archives the tar extract command
tar czvf MyProject.20090816.tgz MyProject // You can compress a tar archive with the gzip command after you create it

12. top command is an interactive utility that displays a character-based screen of all processes running on the current system

13. who command lets you display the users that are currently logged into your Unix computer system
$ who

14. ps command by itself, it only shows very basic information about the processes you are currently running
$ps

15. df command stands for "disk free". It is meant to show Linux disk space information, including disk space that is used, disk space remaining, and how filesystems are mounted on your Linux (or Unix) system
$ df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/vzfs 10485760 5713424 4772336 55% /

16. du command shows disk usage information about only the files and directories you specify

17. lsof command lists information about files that are open by processes running on the system. (The lsof command itself stands for “list of open files.”)

18. chmod command name stands for "change mode", and as that name implies, the chmod command is used to change the mode of Unix/Linux files.

chmod +x myShellScript.sh // is commonly used to make a file "executable"
chmod +r myfile.txt // use of the chmod command is to make a file "readable". If a file doesn't have read permission, you can add read permission to that file
chmod +w myfile.txt // In the same way, you can also give a file write permission

19. cp command to copy files and directories on Linux systems

cp source destination // This cp command copies the original file named source to the new file named destination. After issuing this command both your original file and the new file will be in the current directory.
cp -r Foo /tmp // You can also copy directories with the Linux cp command, and when you do this, you just need to remember to use the -r option

20. uname // Stands for Unix name - print detailed information about the machine name, Operating System and Kernel.

root@techchai:~# uname -a
Linux techchai 3.8.0-19-generic #30-Ubuntu SMP Wed May 1 16:36:13 UTC 2013 i686 i686 i686 GNU/Linux

21. history command is used to prints the history of long list of executed commands in terminal.

Android Interview Questions

2018-12-22T19:14:00.002-08:00

https://coderinsight.blogspot.com/2018/12/android-interview-questions.html

Java Interview Questions

2018-12-22T19:07:00.003-08:00

1) Explain OOP Concepts
2) Differences between abstract classes and interfaces?
3) What is the difference between iterator and enumeration in java?
4) Composition vs Inheritance
5) Difference between method overloading and overriding
6) What are the access modifiers you know? What does each one do?
7) Can an Interface implement another Interface?
8) What is Polymorphism? What is Inheritance?
9) Explain Generics in Java?
10) Stack vs Queue
11) HashMap vs Set
12) HashSet vs TreeSet
13) What is Java PriorityQueue?
14) How is String class implemented? Why was it made immutable?
15) What does it means to say that a String is immutable?
16) What is String.intern()? When and why should it be used?
17) Can you list primitive types in Java?
18) What is the difference between an Integer and int?
19) What is Autoboxing and Unboxing?
20) Typecast in Java?
21) Do objects get passed by reference or value in Java? Elaborate on that.
22) What is the difference between instantiation and initialization of an object?
23) What the difference between local, instance and class variables?
24) What is garbage collector? How does it work?
25) What is memory leak and how does Java handle it?
26) What are strong, soft, weak and phantom references in Java?
27) What does the keyword synchronized mean?
28) What is a ThreadPoolExecutor?
29) What is volatile modifier?
30) How does the try{} catch{} finally{} works?
31) What is the difference between a Checked Exception and an Un-Checked Exception?
32) What is serialization? How do you implement it?
33) What is transient modifier?
34) What are anonymous classes?
35) What is the difference between using == and .equals on an object?
36) What is the hashCode() and equals() used for?
37) Why would you not call abstract method in constructor?
38) When would you make an object value final?
39) What are these final, finally and finalize keywords?
40) What does the static word mean in Java?
41) Can a static method be overridden in Java?
42) When is a static block run?
43) What is reflection?
44) How is a StringBuilder implemented to avoid the immutable string allocation problem?
45) Difference between StringBuffer and StringBuilder?
46) What’s the difference between an Enumeration and an Iterator?
47) What is the difference between fail-fast and fail-safe iterators in Java?
48) What do you mean by platform independence of Java?
49) What is the difference between JDK and JVM?
50) Which class is the superclass of all classes?
51) Why Java doesn’t support multiple inheritance?
52) Why Java is not pure Object Oriented language?
53) What is the importance of main method in Java?
54) Can we overload main method?
55) Can we have multiple public classes in a java source file?
56) What is Java Package and which package is imported by default?
57) What are access modifiers?
58) What is final keyword?
59) What is static keyword?
60) Can we declare a class as static?
61) What are Wrapper classes?
62) What is Enum in Java?
63) What is composition in java?
64) What does super keyword do?
65) What is this keyword?
66) What is break and continue statement?
67) What is default constructor?
68) Can we have try without catch block?
69) What is the use of System class?
70) What is instanceof keyword?
71) What is difference between Heap and Stack Memory?

Python Interview Questions

2017-05-21T16:20:00.002-07:00

1) What is Python? What are the benefits of using Python and its main features?
2) What is PEP 8?
3) What Are The Built-In Types Available In Python?
4) What is mutable and immutable objects in python?
5) Difference between remove, pop, del on lists?
6) What is the difference between list and tuple?
7) What are tuples?
8) What is difference between tuple and list ? Where will you use tuple and where will you use list ?
9) What is Dynamic Typing ?
10) What are *args, **kwargs ?
11) How instance variables are different from class variables?
12) Differentiate between “*.py” file and “*.pyc” file?
13) Explain the use “with” statement in python?
14) What does the “self” keyword do?
15) What Are Different Methods To Copy an Object In Python?
16) What does the <yield> keyword do in Python?
17) What is pickling and unpickling?
18) How are arguments passed by value or by reference?
19) What is namespace in Python?
20) How you can convert a number to a string?
21) What is module and package in Python?
22) What is a pass in Python?
23) Write a function to merge the two lists into one sorted list:
X = [2, 5, 7, 10, 11, 18]
Y = [1, 4, 6, 12, 14, 17, 21]
24) How can we get home directory using '~' in Python?
25) Difference between range and xrange?
26) Generators in Python and its use?
27) What are Iterators ?
28) How to debug python code using PDB?
29) What Lambda and use in Python?
30) How does Python handle the memory management?
31) What is monkey patching? How can you do it in Python?
32) Why are functions considered first class objects in Python?
33) How will you reverse the list in Python?
34) Explain how can you generate random numbers in Python?
35) Explain the usage of decorators?

What is Data structure?

2016-12-20T19:20:00.000-08:00

Data structure is a method of organizing large amount of data more efficiently so that any operation on that data becomes easy.

Data structures are divided into two types:

Linear Data Structures
Non linear Data structures

Linear Data Structure: In Linear data structure, data is organised in sequential order.
Ex: Arrays, Linked list, Stacks and Queues

Non Linear Data Structure: In Non Linear data structure, data is organised in random order.
Ex: Tree, Graphs

Interrupt Handling in Linux

2016-04-17T18:52:00.003-07:00

What is Interrupt?

An interrupt (also known as an exception or trap) is an event that causes the CPU to stop executing the current program and start executing a special piece of code called an interrupt handler or interrupt service routine (ISR).

There are two different kinds of interrupts:

•Synchronous interrupt (Exception) produced by the CPU while processing instructions
•Asynchronous interrupt (Interrupt) issued by other hardware devices

Handling interrupts:
•Interrupts can occur at any time, the kernel tries to get it out of the way as soon as possible
•An interrupt can be interrupted by another interrupt
•There are regions in the kernel which must not be interrupted at all

Two different interrupt levels are defined:
•Maskable interrupts issued by I/O devices; can be in two states, masked or unmasked. Only unmasked interrupts are getting processed.
•Nonmaskable interrupts; critical malfunctions (f.e. hardware failure); always processed by the CPU.

Every hardware device has it's own Interrupt Request (IRQ) line. The IRQs are numbered starting from 0. All IRQ lines are connected to a Programmable Interrupt Controller (PIC). The PIC listens on IRQs and assigns them to the CPU. It is also possible to disable a specific IRQ line.

Top Half and Bottom Half:

One of the main problems with interrupt handling is how to perform lengthy tasks within a handler. Often a substantial amount of workmust be done in response to a device interrupt, but interrupt handlers need to finish up quickly and not keep interrupts blocked for long. These two needs (work and speed) conflict with each other,leaving the driver writer in a bit of a bind.

Linux (along with many other systems) resolves this problem by splitting the interrupt handler into two halves. The so-called top half is the routine that actually responds to the interrupt—the one you register with request_irq. The bottom half is a routine that is scheduled by the top half to be executed later, at a safer time. The big difference between the top-half handler and the bottom half is that all interrupts are enabled during execution of the bottom half—that’s why it runs at a safer time.

To implement bottom halves,two methods:
1) task lets
2) work queues

Linux Kernel Modules

2016-04-17T18:50:00.001-07:00

Linux kernel modules are pieces of code that can be loaded and unloaded from kernel on demand.

Kernel modules offers an easy way to extend the functionality of the base kernel without having to rebuild or recompile the kernel again. Most of the drivers are implemented as a Linux kernel modules. When those drivers are not needed, we can unload only that specific driver, which will reduce the kernel image size.

Kernel modules will have extension .ko
Kernel modules will operate on kernel space.
All Drivers are modules. Not all modules are drivers.

Kernel Modules Commands:
lsmod: To see list of modules that already loaded on system
insmod: To insert modules into kernel
modinfo: To display modules information
rmmod: To remove modules from kernel
How to Write Kernel Modules:
module.c

#include <linux/module.h>    // included for all kernel modules
#include <linux/kernel.h>    // included for KERN_INFO
#include <linux/init.h>      // included for __init and __exit macros

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Name");
MODULE_DESCRIPTION("Hello World module");

static int __init hello_init(void)
{
    printk(KERN_INFO "Hello world!\n");
    return 0;    // Non-zero return means that the module couldn't be loaded.
}

static void __exit hello_cleanup(void)
{
    printk(KERN_INFO "Cleaning up module.\n");
}

module_init(hello_init);
module_exit(hello_cleanup);

Makefile to compile module:

obj-m += hello.o

all:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

When a module is inserted into the kernel, the module_init macro will be invoked, which will call the function hello_init. Similarly, when the module is removed with rmmod, module_exit macro will be invoked, which will call the hello_exit. Using dmesg command, we can see the output from the sample Kernel module.

printk() is used for printing kernel messages

Latest Kernel version

2016-04-17T18:26:00.002-07:00

Current stable kernel version: 4.5.1
https://www.kernel.org/

C program to reverse an array

2014-09-05T20:30:00.000-07:00

#include  
int main() 
{ 
      int n, c, d, a[100], b[100]; 
      printf("Enter the number of elements in array\n"); 
      scanf("%d", &n); 
      printf("Enter the array elements\n"); 
      for (c = 0; c < n ; c++) 
           scanf("%d", &a[c]); 
      for (c = n - 1, d = 0; c >= 0; c--, d++) 
           b[d] = a[c]; 
      for (c = 0; c < n; c++) 

           a[c] = b[c]; 

      printf("Reverse array is\n"); 

      for (c = 0; c < n; c++) 

      printf("%d\n", a[c]);
 
 return 0; 

}

This program reverses the array elements. For example if a is an array of integers with three elements such that
a[0] = 1
a[1] = 2
a[2] = 3

Then on reversing the array will be
a[0] = 3
a[1] = 2
a[0] = 1

C++; Singleton Design Pattern

2014-08-15T09:39:00.002-07:00

Singleton is a creational design pattern.
Provide one and only instance of an object.

#include using namespace std;

class MySingleton

{

public: static MySingleton* iInstance;

public: static MySingleton* GetInstance();

private: MySingleton();

};

MySingleton* MySingleton::iInstance = NULL;

MySingleton::MySingleton()

{

cout << "Inside construtor ..." << endl;

}

MySingleton* MySingleton::GetInstance()

{

if ( iInstance == NULL )

{

iInstance = new MySingleton();

}

return iInstance;

}

void main()

{

MySingleton* obj;

obj = MySingleton::GetInstance();

}

Useful linux commands

2014-08-02T12:50:00.000-07:00

Vi Editor:

x Delete character at cursor
X Delete character before cursor
Y or yy Yank (copy) current line into "unnamed" storage buffer.
p Paste unnamed storage buffer after current line.
P Paste unnamed storage buffer before current line.
r Replace character
R Overwrite characters from cursor onward
s Substitute one character under cursor continue to insert
S Substitute entire line and begin to insert at beginning of line
J Join current and following line into one line

Use command: ":e filename"

Start new edit session on specified file name without closing current vi / vim editor process.

Find/Replace:Example:

:%s/fff/rrrrr/ - For all lines in a file, find string "fff" and replace with string "rrrrr" for the first instance on a line.

:%s/fff/rrrrr/g - For all lines in a file, find string "fff" and replace with string "rrrrr" for each instance on a line.

:%s/fff/rrrrr/gc - For all lines in a file, find string "fff" and replace with string "rrrrr" for each instance on a line. Ask for confirmation
:%s/fff/rrrrr/gi - For all lines in a file, find string "fff" and replace with string "rrrrr" for each instance on a line. Case insensitive.

Extract or Unpack a tar File:

To extract tar file of type:

tar -xvf <filename>.tar

To extract .tar.gz (gzip) file

tar -xzvf <file name>.tar.gz
To extract .tar.bz2 (bzip2) file

tar -xjvf file.tar.bz2

To extarct single file from tar file

tar -xvf file.tar foo.txt

tar -xzvf file.tar.gz foo.txt

tar -xjvf file.tar.bz2 foo.txt

Where,
-x : Extract a tar ball.
-v : Verbose output or show progress while extracting files.
-f : Specify an archive or a tarball filename.
-j : Decompress and extract the contents of the compressed archive created by bzip2 program (tar.bz2 extension).
-z : Decompress and extract the contents of the compressed archive created by gzip program (tar.gz extension).

C++ Tips

2013-05-05T04:21:00.001-07:00

Class is collection of data members and member fn.
Object is a instance of a class
Abstraction is hiding unessential things and reveal the essential things.
Encapsulation is wrapping up data and functions into a single unit Abstraction implies encapsulation.(Relationship between Abstraction and Encapsulation)
Inheritance is a process of crating new class form existing class. The new class is called Derived class and the old class is called Base class Inheritance is mainly used to code reusability.In multiple inheritance occur an ambiguity error. But multilevel inheritance not occur an ambiguity error.
Composite is a opposite of Inheritance. It’s used to related between two distinct classes (unrelated classes).
Function overloading function having same name with different signature in same class.
Operator overloading means to work on a different operand.
Function overriding function having same name with same signature in different class.
Polymorphism is ability to assure several distinct forms(tasks). There are two type of polymorphism is available

i. static or compile time Polymorphism

(Operator overloading and function overloading)

ii.Dynamic or run time Polymorphism ( Virtual function)

Virtual functions work in overridden technique. Virtual fn is mainly used to, base class pointer can access derived class functions.

Abstract class means, a class which contain at least one pure virtual function. In abstract class cannot create an object.

Pure virtual function is a virtual function with expression equal to zero in declaration part.

Macro is a single line replacement of set of statements.

Inline is a keyword , its appear before function name. This function is faster than normal function. Inline function is a single line replacement of set of statements.

Both (macro and inline function) functions are replaced a set of

statement. The statements are replaced in Pre-compilation Time

(Before compilation).

Inline functions are used in Type checking like normal function. But macro won’t (Difference)

In structure , the default access specifies is Public. But class , is Private (Difference)

In structure, the data members are associated in separate memory. But Union, data members are shared in common memory. The size of union = Largest data member size in union (Difference).

New is operator, it’s overloaded, it’s call constructor automatically. But malloc() is not overloaded and it’s cannot call constructor. But both are allocate memory.(Difference)

Malloc() and calloc() both are allocate memory. But malloc() allocate memory and store(initialize) the garbage value. But calloc() allocate memory, its allocate integer type then initialize zero its string initialize NULL value. (Difference)

Delete statement delete the all elements in an array, but the destructor call only the first element.delete[] statement delete the all element in an array, the destructor call each and every element in an array.(Difference)

Delete is a operator, it can be overload. Its call destructor call automatically. Delete operator mainly used to de-allocate memory.

New is a operator , its overload operator. Its call constructor automatically. New operator mainly used to allocate memory.

Constructor is call automatically, whenever an object is created then the constructor is call. Constructor is overload, it cannot return a value, and return type.

Destructor is a call automatically, whenever an object is destroyed then the destructor will call.Its can’t overloaded, its cannot return a value and return type.

this pointer is a constant pointer. Its can use only non static member function. Its cannot used in static member function, because the static function share in all object but the this pointer points the current object.

Explain this:

Ø int (*p)[10] ------ Pointer to array , first preference in pointer

Ø int *p[10] ------ Array of pointer to int value , first preference in array

Ø int *f() ------ function pointer

Ø int (*f)() ------ pointer to function

Which is the best sorting method?

2013-05-05T04:07:00.001-07:00

There is no sorting method that is universally superior to all others. The programmer must carefully examine the problem and the desired results before deciding the particular sorting method. Some of the sorting methods are given below:

Bubble sort : When a file containing records is to be sorted then Bubble sort is the best sorting method when sorting by address is used.

Bsort : It can be recommended if the input to the file is known to be nearly sorted.

Meansort : It can be recommended only for input known to be very nearly sorted.

Quick Sort : In the virtual memory environment, where pages of data are constantly being swapped back and forth between external and internal storage. In practical situations, quick sort is often the fastest available because of its low overhead and its average behavior.

Heap sort : Generally used for sorting of complete binary tree. Simple insertion sort and straight selection sort : Both are more efficient than bubble sort. Selection sort is recommended for small files when records are large and for reverse situation insertion sort is recommended. The heap sort and quick sort are both more efficient than insertion or selection for large number of data.

Shell sort : It is recommended for moderately sized files of several hundred elements.

Radix sort : It is reasonably efficient if the number of digits in the keys is not too large.

Is it possible that one try block can have multiple catch blocks?

2013-05-05T04:04:00.000-07:00

There can be more than one exception handler (or catch block) for one try block, because it might so happen that in one single try block there can be different types of exceptions that can be thrown.

This is shown in the following code snippet:

try
{

// statement that throws divide-by-zero exception
// statement that throws array out-of-bound exception

}
catch ( divide_error id1 ){ // code }
catch ( out_of_bound_error id2 ){ // code }

Is it possible to throw an exception through a constructor?

2013-05-05T04:01:00.000-07:00

Yes, we can! We cannot return any error value from the constructor, as the constructor doesn’t have any return type. In such situation, by throwing an exception we can pass value to catch block.

This is shown in the following example:

#include <iostream.h>
class sample

{

public:

sample ( int i )

{

if ( i == 0 ) throw "error";

}

};
void main( )

{

try

{

sample s ( 0 );

}
catch ( char * str )

{

cout << str;

}

How can we copy the contents of one file to another in one shot?

2013-05-05T03:27:00.002-07:00

#include <fstream.h>

void main( )

{

char source [ 67 ], target [ 67 ];
char ch;
cout << endl << "Enter source filename";
cin >> source;
cout << endl << "Enter target filename";
cin >> target;
ifstream infile ( source );
ofstream outfile ( target );
outfile << infile.rdbuf( );

}

Here all the copying is done through the single statement

outfile << infile.rdbuf( );

The function rdbuf( ) returns the address of the strstreambuf where the values are stored.

How to allocate memory for a multidimensional array dynamically?

2013-05-05T03:24:00.000-07:00

Many times we need to allocate memory for a multidimensional array dynamically. Because of complexity of pointers many find this difficult.

Following program allocates memory for a 3 x 3 array dynamically, copies contents of a 3 x 3 array in it and prints the contents using the pointer.

#include <iostream.h>

#include <new.h>

int a[ ][3] = {

1, 2, 3,

4, 5, 6,

7, 8, 9

};

void main( )

{

int **p;

p = new int *[3] ;

for ( int i = 0 ; i < 3 ; i++ )

p[i] = new int[3];

for ( i = 0 ; i < 3 ; i++ )

for ( int j = 0 ; j < 3 ; j++ )

p[i][j] = a[i][j] ;

for ( i = 0 ; i < 3 ; i++ )

{

for ( j = 0 ; j < 3 ; j++ )

cout << p[i][j] ;

cout << "\n" ;

}

How do I change a data member of the const object?

2013-05-05T03:17:00.003-07:00

To change the data members of the const object the data members are declared as mutable in the class.

This is shown in the following example:

#include <iostream.h>

class sample

{

private :

mutable int i;

public :

sample( int ii = 0 )

{

i = ii;

}

void fun( ) const

{

i++;

cout<< i;

}

};

void main( )

{

const sample s ( 15 ) ;

s.fun( );

}

Here, the object s is const and hence only const functions can operate upon it. When the const function fun( ) gets called to operate upon object s, the data member i is incremented. Ideally the data member should not be changed, as object is defined const. But we can change the data member i because it is declared as mutable in the class sample

Why is it necessary to use a reference in the argument to the copy constructor?

2013-05-05T03:14:00.001-07:00

If we pass the copy constructor the argument by value, its copy would get constructed using the copy constructor. This means the copy constructor would call itself to make this copy. This process would go on and on until the compiler runs out of memory.

This can be explained with the help of following example:

class sample

{

int i;

public:

sample (sample p)

{

i = p.i;

}

};

void main( )

{

sample s;

sample s1(s);

}

While executing the statement sample s1 ( s ), the copy constructor would get called. As the copy construct here accepts a value, the value of s would be passed which would get collected in p. We can think of this statement as sample p = s. Here p is getting created and initialized. Means again the copy constructor would get called. This would result into recursive calls.Hence we must use a reference as an argument in a copy constructor.

How do I write code that allows to create only one instance of a class?

2013-05-05T03:10:00.000-07:00

#include <iostream.h>

class sample

{

static sample *ptr ;

private:

sample( ){}

public:

static sample* create( )

{

if ( ptr == NULL )

ptr = new sample ;

return ptr;

}

} ;

sample *sample::ptr = NULL ;

void main( )

{

sample *a = sample::create( ) ;

sample *b = sample::create( ) ;

}

Here, the class sample contains a static data member ptr which is a pointer to the object of same class. The constructor is private which avoids us from creating objects outside the class. A static member function called create( ) is used to create an object of the class. In this function the condition is checked whether or not ptr is NULL, if it is then an object is created dynamically and its address collected in ptr is returned. If ptr is not NULL, then the same address is returned. Thus, in main( ) on execution of the first statement one object of sample gets created whereas on execution of second statement, b holds the address of the first object. Thus, whatever number of times you call create( ) function, only one object of sample class will be available.

Most Commonly Used Git Commands

2013-04-25T05:24:00.002-07:00

usage: git [--version] [--exec-path[=<path>]] [--html-path] [--man-path] [-- info-path] [-p|--paginate|--no-pager] [--no-replace-objects] [--bare]
[--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
[-c name=value] [--help] <command> [<args>]

The most commonly used git commands are:
add Add file contents to the index
bisect Find by binary search the change that introduced a bug
branch List, create, or delete branches
checkout Checkout a branch or paths to the working tree
clone Clone a repository into a new directory
commit Record changes to the repository
diff Show changes between commits, commit and working tree, etc
fetch Download objects and refs from another repository
grep Print lines matching a pattern
init Create an empty git repository or reinitialize an existing one
log Show commit logs
merge Join two or more development histories together
mv Move or rename a file, a directory, or a symlink
pull Fetch from and merge with another repository or a local branch
push Update remote refs along with associated objects
rebase Forward-port local commits to the updated upstream head
reset Reset current HEAD to the specified state
rm Remove files from the working tree and from the index
show Show various types of objects
status Show the working tree status
tag Create, list, delete or verify a tag object signed with GPG

Git: Installation & Setup

2013-04-24T02:41:00.000-07:00

Installation:

1) Ubuntu,debian
sudo apt-get install git-core
2) Fedora,red hat
yum install git

3) Windows
http://code.google.com/p/msysgit/
4) Mac OS
http://code.google.com/p/git-osx-installer

Setting up Git:

When you first start using Git, there are a few things you will likely want to get setup before you start. Git records your name and email address when you create commits, so you need to tell Git what those are.

You can use the git config command to set those. If you pass --global, it will save the values in the ‘~/.gitconfig’ file so they are the default for all of your repositories.

User Configuration:

$ git config --global user.name "Your Name"

$ git config --global user.email "YourMail@gmail.com"

Push configuration:

The following command configure Git so that the git push command pushes always all branches which are connected to a remote branch (configured as remote tracking branches) to your Git remote repository. This makes is typical easier to ensure that all relevant branches are pushed.

# set default so that all changes are always pushed to the repository

$ git config --global push.default "matching"

Avoid merge commits for pulling:

If you pull in changes from a remote repository, Git by default creates merge commits. This typically undesired and you can avoid this via the following setting.

# set default so that you avoid unnecessary commits

$ git config --global branch.autosetuprebase always

Color Highlighting:

$ git config --global color.ui true

$ git config --global color.status auto

$ git config --global color.branch auto

Setting the default editor:

$ git config --global core.editor vim

What is Git?

2013-04-24T02:09:00.004-07:00

Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.

Git allows groups of people to work on the same documents (often code) at the same time, and without stepping on each other's toes. It's a distributed version control system.

Git is a distributed system, everyone has their own copy of the source codes.

Distributed version control system:

A distributed version control system has not necessary a central server which stores the data.

The user can copy an existing repository. This copying process is typically called cloning in a distributed version control system.

Typically there is a central server for keeping a repository but each cloned repository is a full copy of this repository. The decision which of the copies is considered to be the central server repository is a pure convention and not tied to the capabilities of the distributed version control itself.

Every local copy contains the full history of the collection of files and a cloned repository has the same functionality as the original repository.

Every repository can exchange versions of the files with other repositories by transporting these changes. This is typically done via the selected central server repository.

C Program to Print a pyramid string triangle

2013-04-23T22:08:00.002-07:00

#include <stdio.h>
#include <string.h>
int main()
{
int i,j,length;
char arr[] = "Programming";
length = strlen(arr);
for (i = length; i >= 0; i--)
{
printf("\n");
for (j = 0; j< i; j++)
{
printf("%c",arr[j]);
}
}
return 0;
}

Output:

Programming

Programmin

Programmi

Programm

Program

Progra

Progr

Prog

Pro