Inheritance in CSS

CSS Inheritance

An explanation of how inheritance works in CSS and why CSS doesn't need Object Oriented style inheritance.
Introduction

Many newcomers to CSS are confused by inheritance; this is often because they come from a background in object oriented (OOP) programming and expect CSS to work in a similar way.

This document attempts to explain CSS inheritance and present alternatives to OO-style inheritance to demonstrate why it is not necessary.
CSS Inheritance

CSS inheritance works on a property by property basis. When applied to an element in a document, a property with the value 'inherit' will use the same value as the parent element has for that property.

For example, given this style sheet:

`.foo {
background-color: white;
color: black;
}

`.bar {
background-color: inherit;
color: inherit;
font-weight: normal;
}

And this HTML fragment:

div class="foo">

Hello, world. This is a very short
paragraph!

`div>

The background colour of the div element is white, because the background-color property is set to white. The background colour of the paragraph is also white, because the background colour property is set to inherit, and the background colour of the parent element (the div) is set to white.

The inherit value does not require that the parent element have the same property set explicitly; it works from the computed value. In the above example, the color property of the paragraph has a value of "inherit", but the computed value is "black" because it inherits.

This might seem like a lot of typing, but the default value for many properties is already inherit, and for most others (border for instance) you wouldn't usually want to inherit the parent element's value.

While on that line of thought, I'll point out that not all properties can be inherited.
Object Oriented inheritance

Many people ask on mailing lists and in newsgroups about CSS if it is possible to do something such as:

`.foo {
background-color: white;
color: black;
}

`.bar {
Some reference to the above style for .foo
font-weight: normal;
}

It isn't. A selector is just a selector, there is nothing special about classes. Things would get rather complex if you had .foo > .bar as the selector for a style you wanted to import, or multiple identical selectors.

I won't go into how CSS could be changed to allow such functionality, not only would there be a lack of support among today's generation of browsers (which are likely to be with us for a long time to come), but it isn't needed. CSS already gives us the tools we need.

There are several approaches we could take.
Multiple Classes

Making good use of classes will solve most problems. Take the example of having boxes of data floating on alternating sides of the canvas.

`.oddBoxOut {
width: 12em;
float: left;
padding: 0.5em;
margin: 0.5em;
border: solid 1px black;
}

`.evenBoxOut {
width: 12em;
float: right;
padding: 0.5em;
margin: 0.5em;
border: solid 1px black;
}

As you can see, many properties are duplicated in each definition, so it is obvious why somebody might want OO-style inheritance.

There is another solution though. Lets take a quick look back at the HTML specification:

` class = cdata-list[CS]
This attribute assigns a class name or set of class names to an element. Any number of elements may be assigned the same class name or names. Multiple class names must be separated by white space characters.

So we can assign multiple class names to a single element? That means we can change the style sheet so it looks like this:

`.boxOut {
width: 12em;
padding: 0.5em;
margin: 0.5em;
border: solid 1px black;
}

`.oddBoxOut {
float: left;
}

`.evenBoxOut {
float: right;
}

And then the HTML will look like:

`div class="boxOut oddBoxOut">div>

Grouping Selectors

A single style may have multiple selectors assigned to it through the use of grouping.

To revisit the previous example, we first simplify the HTML so we only mention the one class:

div class="oddBoxOut">div>

Then we assign the CSS we want to it, but we group the common property/value pairs.

`.oddBoxOut,
`.evenBoxOut {
width: 12em;
padding: 0.5em;
margin: 0.5em;
border: solid 1px black;
}

`.oddBoxOut {
float: left;
}

`.evenBoxOut {
float: right;
}

These two techniques should solve most problems which people think can be solved with OO-style inheritance

Algorithm Interview questions Answers ( Microsoft, Google and Amazon )

1. Reverse a singly linked list


//
// iterative version
//
Node* ReverseList( Node ** List )
{

Node *temp1 = *List;
Node * temp2 = NULL;
Node * temp3 = NULL;

while ( temp1 )
{
*List = temp1; //set the head to last node
temp2= temp1->pNext; // save the next ptr in temp2
temp1->pNext = temp3; // change next to privous
temp3 = temp1;
temp1 = temp2;
}

return *List;
}


2. Delete a node in double linked list


void deleteNode(node *n)
{
node *np = n->prev;
node *nn = n->next;
np->next = n->next;
nn->prev = n->prev;
delete n;
}


3. Sort a linked list

//sorting in descending order
struct node
{
int value;
node* NEXT;
}
//Assume HEAD pointer denotes the first element in the //linked list
// only change the values…don’t have to change the //pointers

Sort( Node *Head)
{
node* first,second,temp;
first= Head;
while(first!=null)
{
second=first->NEXT;
while(second!=null)
{
if(first->value < second->value)
{
temp = new node();
temp->value=first->value;
first->value=second->value;
second->value=temp->value;
delete temp;
}
second=second->NEXT;
}

first=first->NEXT;
}
}


4. Reverse a string

void ReverseString (char *String)
{
char *Begin = String;
char *End = String + strlen(String) - 1;
char TempChar = '\0';

while (Begin < End)
{
TempChar = *Begin;
*Begin = *End;
*End = TempChar;
Begin++;
End--;
}
}


5. Insert a node a sorted linked list

void sortedInsert(Node * head, Node* newNode)
{
Node *current = head;

// traverse the list until you find item bigger the // new node value
//
while (current!= NULL && current->data < newNode->data)
{
current = current->next);
}
//
// insert the new node before the big item
//
newNode->next = current->next;
current = newNode;
}



6. Covert a string to upper case

void ToUpper(char * S)
{
while (*S!=0)
{
*S=(*S >= 'a' && *S <= 'z')?(*S-'a'+'A'):*S;
S++;
}
}


7. Multiple a number by 7 without using * and + operator.

NewNum = Num << 3; // mulitplied by 2 ^ 3 = 8

NewNum = NewNum - Num; // 8 – 1 = 7


8. Write a function that takes in a string parameter and checks to see whether or not it is an integer, and if it is then return the integer value.

#include

int strtoint(char *s)
{
int index = 0, flag = 0;

while( *(s+index) != '\0')
{
if( (*(s + index) >= '0') &&
*(s + index) <= '9')
{
flag = 1;
index++;
}
else
{
flag = 0;
break;
}
}

if( flag == 1 )
return atoi(s);
else
return 0;
}

main()
{
printf("%d",strtoint("0123"));
printf("\n%d",strtoint("0123ii"));
}



9. Print a data from a binary tree – In-order(ascending)

//
// recursive version
//

Void PrintTree ( struct * node node )
{
if ( node == NULL )
return;

PrintTree(node->left );
Printf(“%d”, node->data);
PrintTree(node->right );
}

10. print integer using only putchar

//
// recursive version
//
void PrintNum ( int Num )
{
if ( Num == 0 )
return;
PrintNum ( Num / 10 );
Puthcar ( ‘0’+ Num % 10 );
}

11. Find the factorial of number

//
// recursive version
//

int Factorial( int Num )
{

If ( num > 0 )
return Num * Factorial ( Num –1 );
else
return 1;
}


//
// iterative version
//

int Factorial( int Num )
{
int I
int result = 1;

for ( I= Num; I > 0; I-- )
{
result = result * I;
}

return result;
}


12. Generate Fib numbers:

int fib( n ) // recursive version
{

if ( n < 2 )
return 1;
else
return fib ( n –1 ) + fib ( n –2 );

}

int fib( n ) //iterative version
{
int f1 =1, f2 = 1;

if ( n < 2 )
return 1;
for ( i = 1; i < N; i++)
{
f = f1 + f2;
f1= f2;
f = f1;
}

return f;
}







13. Write a function that finds the last instance of a character in a string

char *lastchar(char *String, char ch)
{
char *pStr = NULL;

// traverse the entire string

while( * String ++ != NULL )
{
if( *String == ch )
pStr = String;
}

return pStr;
}

14. Return Nth the node from the end of the linked list in one pass.

Node * GetNthNode ( Node* Head , int NthNode )
{
Node * pNthNode = NULL;
Node * pTempNode = NULL;
int nCurrentElement = 0;

for ( pTempNode = Head; pTempNode != NULL; pTempNode = pTempNode->pNext )
{
nCurrentElement++;
if ( nCurrentElement - NthNode == 0 )
{
pNthNode = Head;
}
else
if ( nCurrentElement - NthNode > 0)
{
pNthNode = pNthNode ->pNext;
}
}
if (pNthNode )
{
return pNthNode;
}
else
return NULL;
}



15. Counting set bits in a number.

First version:

int CoutSetBits(int Num)
{

for(int count=0; Num; Num >>= 1)
{
if (Num & 1)
count++;
}
return count;
}


Optimized version:

int CoutSetBits(int Num)
{

for(int count =0; Num; count++)
{
Num &= Num -1;
}
}

C++ Microsoft and Amazon interview Questions

What is encapsulation??
Containing and hiding information about an object, such as internal data structures and code. Encapsulation isolates the internal complexity of an object's operation from the rest of the application. For example, a client component asking for net revenue from a business object need not know the data's origin.

What is inheritance?
Inheritance allows one class to reuse the state and behavior of another class. The derived class inherits the properties and method implementations of the base class and extends it by overriding methods and adding additional properties and methods.
What is Polymorphism??

Polymorphism allows a client to treat different objects in the same way even if they were created from different classes and exhibit different behaviors.
You can use implementation inheritance to achieve polymorphism in languages such as C++ and Java.
Base class object's pointer can invoke methods in derived class objects.
You can also achieve polymorphism in C++ by function overloading and operator overloading.

What is constructor or ctor?
Constructor creates an object and initializes it. It also creates vtable for virtual functions. It is different from other methods in a class.

What is destructor?
Destructor usually deletes any extra resources allocated by the object.

What is default constructor?
Constructor with no arguments or all the arguments has default values.

What is copy constructor?
Constructor which initializes the it's object member variables ( by shallow copying) with another object of the same class. If you don't implement one in your class then compiler implements one for you.
for example:
Boo Obj1(10); // calling Boo constructor
Boo Obj2(Obj1); // calling boo copy constructor
Boo Obj2 = Obj1;// calling boo copy constructor

When are copy constructors called?
Copy constructors are called in following cases:
a) when a function returns an object of that class by value
b) when the object of that class is passed by value as an argument to a function
c) when you construct an object based on another object of the same class
d) When compiler generates a temporary object

What is assignment operator?
Default assignment operator handles assigning one object to another of the same class. Member to member copy (shallow copy)
What are all the implicit member functions of the class? Or what are all the functions which compiler implements for us if we don't define one.??
default ctor
copy ctor
assignment operator
default destructor
address operator

What is conversion constructor?
constructor with a single argument makes that constructor as conversion ctor and it can be used for type conversion.
for example:
class Boo
{
public:
Boo( int i );
};
Boo BooObject = 10 ; // assigning int 10 Boo object
What is conversion operator??
class can have a public method for specific data type conversions.
for example:
class Boo
{
double value;
public:
Boo(int i )
operator double()
{
return value;
}
};
Boo BooObject;
double i = BooObject; // assigning object to variable i of type double. now conversion operator gets called to assign the value.

What is diff between malloc()/free() and new/delete?

malloc allocates memory for object in heap but doesn't invoke object's constructor to initiallize the object.

new allocates memory and also invokes constructor to initialize the object.

malloc() and free() do not support object semantics
Does not construct and destruct objects
string * ptr = (string *)(malloc (sizeof(string)))
Are not safe
Does not calculate the size of the objects that it construct
Returns a pointer to void
int *p = (int *) (malloc(sizeof(int)));
int *p = new int;
Are not extensible
new and delete can be overloaded in a class

"delete" first calls the object's termination routine (i.e. its destructor) and then releases the space the object occupied on the heap memory. If an array of objects was created using new, then delete must be told that it is dealing with an array by preceding the name with an empty []:-

Int_t *my_ints = new Int_t[10];

...

delete []my_ints;

what is the diff between "new" and "operator new" ?

"operator new" works like malloc.

What is difference between template and macro??

There is no way for the compiler to verify that the macro parameters are of compatible types. The macro is expanded without any special type checking.

If macro parameter has a postincremented variable ( like c++ ), the increment is performed two times.

Because macros are expanded by the preprocessor, compiler error messages will refer to the expanded macro, rather than the macro definition itself. Also, the macro will show up in expanded form during debugging.

for example:

Macro:

#define min(i, j) (i <>

template:
template
T min (T i, T j)
{
return i <>

What are C++ storage classes?

auto
register
static
extern

auto: the default. Variables are automatically created and initialized when they are defined and are destroyed at the end of the block containing their definition. They are not visible outside that block

register: a type of auto variable. a suggestion to the compiler to use a CPU register for performance

static: a variable that is known only in the function that contains its definition but is never destroyed and retains its value between calls to that function. It exists from the time the program begins execution

extern: a static variable whose definition and placement is determined when all object and library modules are combined (linked) to form the executable code file. It can be visible outside the file where it is defined.

What are storage qualifiers in C++ ?

They are..

const
volatile
mutable

Const keyword indicates that memory once initialized, should not be altered by a program.

volatile keyword indicates that the value in the memory location can be altered even though nothing in the program
code modifies the contents. for example if you have a pointer to hardware location that contains the time, where hardware changes the value of this pointer variable and not the program. The intent of this keyword to improve the optimization ability of the compiler.

mutable keyword indicates that particular member of a structure or class can be altered even if a particular structure variable, class, or class member function is constant.

struct data
{
char name[80];
mutable double salary;
}

const data MyStruct = { "Satish Shetty", 1000 }; //initlized by complier

strcpy ( MyStruct.name, "Shilpa Shetty"); // compiler error
MyStruct.salaray = 2000 ; // complier is happy allowed

What is reference ??

reference is a name that acts as an alias, or alternative name, for a previously defined variable or an object.

prepending variable with "&" symbol makes it as reference.

for example:

int a;
int &b = a;

What is passing by reference?

Method of passing arguments to a function which takes parameter of type reference.

for example:

void swap( int & x, int &amp;amp;amp;amp; y )
{
int temp = x;
x = y;
y = temp;
}

int a=2, b=3;

swap( a, b );

Basically, inside the function there won't be any copy of the arguments "x" and "y" instead they refer to original variables a and b. so no extra memory needed to pass arguments and it is more efficient.

When do use "const" reference arguments in function?

a) Using const protects you against programming errors that inadvertently alter data.
b) Using const allows function to process both const and non-const actual arguments, while a function without const in the prototype can only accept non constant arguments.
c) Using a const reference allows the function to generate and use a temporary variable appropriately.

When are temporary variables created by C++ compiler?

Provided that function parameter is a "const reference", compiler generates temporary variable in following 2 ways.

a) The actual argument is the correct type, but it isn't Lvalue

double Cube(const double & num)
{
num = num * num * num;
return num;

}

double temp = 2.0;
double value = cube(3.0 + temp); // argument is a expression and not a Lvalue;

b) The actual argument is of the wrong type, but of a type that can be converted to the correct type

long temp = 3L;
double value = cuberoot ( temp); // long to double conversion

What is virtual function?

When derived class overrides the base class method by redefining the same function, then if client wants to access redefined the method from derived class through a pointer from base class object, then you must define this function in base class as virtual function.

class parent
{
void Show()
{
cout << "i'm parent" << endl;
}
};

class child: public parent
{
void Show()
{
cout << "i'm child" << endl;
}

};

parent * parent_object_ptr = new child;

parent_object_ptr->show() // calls parent->show() i

now we goto virtual world...

class parent
{
virtual void Show()
{
cout << "i'm parent" << endl;
}
};

class child: public parent
{
void Show()
{
cout << "i'm child" << endl;
}

};

parent * parent_object_ptr = new child;

parent_object_ptr->show() // calls child->show()

What is pure virtual function? or what is abstract class?

When you define only function prototype in a base class without implementation and do the complete implementation in derived class. This base class is called abstract class and client won't able to instantiate an object using this base class.

You can make a pure virtual function or abstract class this way..

class Boo
{
void foo() = 0;
}

Boo MyBoo; // compilation error

What is Memory alignment??

The term alignment primarily means the tendency of an address pointer value to be a multiple of some power of two. So a pointer with two byte alignment has a zero in the least significant bit. And a pointer with four byte alignment has a zero in both the two least significant bits. And so on. More alignment means a longer sequence of zero bits in the lowest bits of a pointer.

What problem does the namespace feature solve?

Multiple providers of libraries might use common global identifiers causing a name collision when an application tries to link with two or more such libraries. The namespace feature surrounds a library's external declarations with a unique namespace that eliminates the potential for those collisions.

namespace [identifier] { namespace-body }

A namespace declaration identifies and assigns a name to a declarative region.
The identifier in a namespace declaration must be unique in the declarative region in which it is used. The identifier is the name of the namespace and is used to reference its members.

What is the use of 'using' declaration?

A using declaration makes it possible to use a name from a namespace without the scope operator.

What is an Iterator class?

A class that is used to traverse through the objects maintained by a container class. There are five categories of iterators: input iterators, output iterators, forward iterators, bidirectional iterators, random access. An iterator is an entity that gives access to the contents of a container object without violating encapsulation constraints. Access to the contents is granted on a one-at-a-time basis in order. The order can be storage order (as in lists and queues) or some arbitrary order (as in array indices) or according to some ordering relation (as in an ordered binary tree). The iterator is a construct, which provides an interface that, when called, yields either the next element in the container, or some value denoting the fact that there are no more elements to examine. Iterators hide the details of access to and update of the elements of a container class. Something like a pointer.

What is a dangling pointer?

A dangling pointer arises when you use the address of an object after its lifetime is over. This may occur in situations like returning addresses of the automatic variables from a function or using the address of the memory block after it is freed.

What do you mean by Stack unwinding?

It is a process during exception handling when the destructor is called for all local objects in the stack between the place where the exception was thrown and where it is caught.

Name the operators that cannot be overloaded??

sizeof, ., .*, .->, ::, ?:

What is a container class? What are the types of container classes?

A container class is a class that is used to hold objects in memory or external storage. A container class acts as a generic holder. A container class has a predefined behavior and a well-known interface. A container class is a supporting class whose purpose is to hide the topology used for maintaining the list of objects in memory. When a container class contains a group of mixed objects, the container is called a heterogeneous container; when the container is holding a group of objects that are all the same, the container is called a homogeneous container.

What is inline function??

The __inline keyword tells the compiler to substitute the code within the function definition for every instance of a function call. However, substitution occurs only at the compiler's discretion. For example, the compiler does not inline a function if its address is taken or if it is too large to inline.

What is overloading??

With the C++ language, you can overload functions and operators. Overloading is the practice of supplying more than one definition for a given function name in the same scope.

- Any two functions in a set of overloaded functions must have different argument lists.
- Overloading functions with argument lists of the same types, based on return type alone, is an error.

What is Overriding?

To override a method, a subclass of the class that originally declared the method must declare a method with the same name, return type (or a subclass of that return type), and same parameter list.
The definition of the method overriding is:
· Must have same method name.
· Must have same data type.
· Must have same argument list.
Overriding a method means that replacing a method functionality in child class. To imply overriding functionality we need parent and child classes. In the child class you define the same method signature as one defined in the parent class.

What is "this" pointer?

The this pointer is a pointer accessible only within the member functions of a class, struct, or union type. It points to the object for which the member function is called. Static member functions do not have a this pointer.

When a nonstatic member function is called for an object, the address of the object is passed as a hidden argument to the function. For example, the following function call

myDate.setMonth( 3 );

can be interpreted this way:

setMonth( &myDate, 3 );

The object's address is available from within the member function as the this pointer. It is legal, though unnecessary, to use the this pointer when referring to members of the class.

What happens when you make call "delete this;" ??

The code has two built-in pitfalls. First, if it executes in a member function for an extern, static, or automatic object, the program will probably crash as soon as the delete statement executes. There is no portable way for an object to tell that it was instantiated on the heap, so the class cannot assert that its object is properly instantiated. Second, when an object commits suicide this way, the using program might not know about its demise. As far as the instantiating program is concerned, the object remains in scope and continues to exist even though the object did itself in. Subsequent dereferencing of the pointer can and usually does lead to disaster.

You should never do this. Since compiler does not know whether the object was allocated on the stack or on the heap, "delete this" could cause a disaster.

How virtual functions are implemented C++?

Virtual functions are implemented using a table of function pointers, called the vtable. There is one entry in the table per virtual function in the class. This table is created by the constructor of the class. When a derived class is constructed, its base class is constructed first which creates the vtable. If the derived class overrides any of the base classes virtual functions, those entries in the vtable are overwritten by the derived class constructor. This is why you should never call virtual functions from a constructor: because the vtable entries for the object may not have been set up by the derived class constructor yet, so you might end up calling base class implementations of those virtual functions

What is name mangling in C++??

The process of encoding the parameter types with the function/method name into a unique name is called name mangling. The inverse process is called demangling.

For example Foo::bar(int, long) const is mangled as `bar__C3Fooil'.
For a constructor, the method name is left out. That is Foo::Foo(int, long) const is mangled as `__C3Fooil'.

What is the difference between a pointer and a reference?

A reference must always refer to some object and, therefore, must always be initialized; pointers do not have such restrictions. A pointer can be reassigned to point to different objects while a reference always refers to an object with which it was initialized.

How are prefix and postfix versions of operator++() differentiated?

The postfix version of operator++() has a dummy parameter of type int. The prefix version does not have dummy parameter.

What is the difference between const char *myPointer and char *const myPointer?

Const char *myPointer is a non constant pointer to constant data; while char *const myPointer is a constant pointer to non constant data.

How can I handle a constructor that fails?

throw an exception. Constructors don't have a return type, so it's not possible to use return codes. The best way to signal constructor failure is therefore to throw an exception.

How can I handle a destructor that fails?

Write a message to a log-file. But do not throw an exception.
The C++ rule is that you must never throw an exception from a destructor that is being called during the "stack unwinding" process of another exception. For example, if someone says throw Foo(), the stack will be unwound so all the stack frames between the throw Foo() and the } catch (Foo e) { will get popped. This is called stack unwinding.
During stack unwinding, all the local objects in all those stack frames are destructed. If one of those destructors throws an exception (say it throws a Bar object), the C++ runtime system is in a no-win situation: should it ignore the Bar and end up in the } catch (Foo e) { where it was originally headed? Should it ignore the Foo and look for a } catch (Bar e) { handler? There is no good answer -- either choice loses information.
So the C++ language guarantees that it will call terminate() at this point, and terminate() kills the process. Bang you're dead.

What is Virtual Destructor?

Using virtual destructors, you can destroy objects without knowing their type - the correct destructor for the object is invoked using the virtual function mechanism. Note that destructors can also be declared as pure virtual functions for abstract classes.

if someone will derive from your class, and if someone will say "new Derived", where "Derived" is derived from your class, and if someone will say delete p, where the actual object's type is "Derived" but the pointer p's type is your class.

Can you think of a situation where your program would crash without reaching the breakpoint which you set at the beginning of main()?

C++ allows for dynamic initialization of global variables before main() is invoked. It is possible that initialization of global will invoke some function. If this function crashes the crash will occur before main() is entered.

Name two cases where you MUST use initialization list as opposed to assignment in constructors.

Both non-static const data members and reference data members cannot be assigned values; instead, you should use initialization list to initialize them.

Can you overload a function based only on whether a parameter is a value or a reference?

No. Passing by value and by reference looks identical to the caller.

What are the differences between a C++ struct and C++ class?

The default member and base class access specifiers are different.

The C++ struct has all the features of the class. The only differences are that a struct defaults to public member access and public base class inheritance, and a class defaults to the private access specifier and private base class inheritance.

What does extern "C" int func(int *, Foo) accomplish?

It will turn off "name mangling" for func so that one can link to code compiled by a C compiler.

How do you access the static member of a class?

::

What is multiple inheritance(virtual inheritance)? What are its advantages and disadvantages?

Multiple Inheritance is the process whereby a child can be derived from more than one parent class. The advantage of multiple inheritance is that it allows a class to inherit the functionality of more than one base class thus allowing for modeling of complex relationships. The disadvantage of multiple inheritance is that it can lead to a lot of confusion(ambiguity) when two base classes implement a method with the same name.

What are the access privileges in C++? What is the default access level?

The access privileges in C++ are private, public and protected. The default access level assigned to members of a class is private. Private members of a class are accessible only within the class and by friends of the class. Protected members are accessible by the class itself and it's sub-classes. Public members of a class can be accessed by anyone.

What is a nested class? Why can it be useful?

A nested class is a class enclosed within the scope of another class. For example:

// Example 1: Nested class
//
class OuterClass
{
class NestedClass
{
// ...
};
// ...
};
Nested classes are useful for organizing code and controlling access and dependencies. Nested classes obey access rules just like other parts of a class do; so, in Example 1, if NestedClass is public then any code can name it as OuterClass::NestedClass. Often nested classes contain private implementation details, and are therefore made private; in Example 1, if NestedClass is private, then only OuterClass's members and friends can use NestedClass.

When you instantiate as outer class, it won't instantiate inside class.

What is a local class? Why can it be useful?

local class is a class defined within the scope of a function -- any function, whether a member function or a free function. For example:

// Example 2: Local class
//
int f()
{
class LocalClass
{
// ...
};
// ...
};
Like nested classes, local classes can be a useful tool for managing code dependencies.

Can a copy constructor accept an object of the same class as parameter, instead of reference of the object?

No. It is specified in the definition of the copy constructor itself. It should generate an error if a programmer specifies a copy constructor with a first argument that is an object and not a reference.

What is encapsulation??

Containing and hiding information about an object, such as internal data structures and code. Encapsulation isolates the internal complexity of an object's operation from the rest of the application. For example, a client component asking for net revenue from a business object need not know the data's origin.

What is inheritance?

Inheritance allows one class to reuse the state and behavior of another class. The derived class inherits the properties and method implementations of the base class and extends it by overriding methods and adding additional properties and methods.

What is Polymorphism??

Polymorphism allows a client to treat different objects in the same way even if they were created from different classes and exhibit different behaviors.

You can use implementation inheritance to achieve polymorphism in languages such as C++ and Java.

Base class object's pointer can invoke methods in derived class objects.

You can also achieve polymorphism in C++ by function overloading and operator overloading.

What is constructor or ctor?

Constructor creates an object and initializes it. It also creates vtable for virtual functions. It is different from other methods in a class.

What is destructor?

Destructor usually deletes any extra resources allocated by the object.

What is default constructor?

Constructor with no arguments or all the arguments has default values.

Few Programming Interview Tips and Tricks ( Amazon and MicroSoft )

Area Number One: Coding

The candidate has to write some code. Give them a coding problem that requires writing a short, straightforward function. They can write it in whatever language they like, as long as they don't just call a library function that does it for them.

It should be a trivial problem, one that even a slow candidate can answer in 5 minutes or less.

(If the candidate seems insulted by the thought of having to get their hands dirty with a trivial coding question, after all their years of experience, patents, etc., tell them it's required procedure and ask them to humor you. If they refuse, tell them we only interview people who can demonstrate coding skills over the phone, thank them for their time, and end the call.)

Give them a few minutes to write and hand-simulate the code. Tell them they need to make it syntactically correct and complete. Make them read the code to you over the phone. Copy down what they read back. Put it into your writeup. If they're sloppy, or don't want to give you exact details, give them one more chance to correct it, and then go with Not Inclined.

(Note added 10/6/04) -- another good approach being used by many teams is to give the candidate "homework". E.g. you can give them an hour to solve some coding problem (harder than the ones below) and email the solution to you. Works like a charm. Definitely preferable to reading code over the phone.

Anyway, here are some examples. I've given solutions in Java, mostly. I've gone back and forth on accepting solutions in other languages (e.g. Ruby, Perl, Python), and I've decided that candidates need to be able to code their answers in C, C++ or Java. It's wonderful if they know other languages, and in fact those who do tend to do a lot better overall. But to be an Amazon SDE, you need to
prove you can do C++ or Java first.

Example 1:   Write a function to reverse a string.

Example Java code:

    public static String reverse ( String s ) {
        int length = s.length(), last = length - 1;
        char[] chars = s.toCharArray();
        for ( int i = 0; i < length/2; i++ ) {
            char c = chars[i];
            chars[i] = chars[last - i];
            chars[last - i] = c;
        }
        return new String(chars);
    }

Example output for "Madam, I'm Adam":   madA m'I ,madaM

Example 2:  Write function to compute Nth fibonacci number:

Java and C/C++:

    static long fib(int n) {
        return n <= 1 ? n : fib(n-1) + fib(n-2);
    }

(Java Test harness)

    public static void main ( String[] args ) {
        for ( int i = 0; i < 10; i++ ) {
            System.out.print ( fib(i) + ", " );
        }
        System.out.println ( fib(10) );
    }

(C/C++ Test Harness)

    main () {
        for ( int i = 0; i < 10; i++ ) {
            printf ( "%d, ", fib(i) );
        }
        printf ( "%d\n", fib(10) );
    }

Test harness output:  

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55

Example 3:  Print out the grade-school multiplication table up to 12x12

Java: (similar for C/C++)

    public static void multTables ( int max )
    {
        for ( int i = 1; i <= max; i++ ) {
            for ( int j = 1; j <= max; j++ ) {
                System.out.print ( String.format ( "%4d", j * i ));
            }
            System.out.println();
        }
    }

Example output:

   1   2   3   4   5   6   7   8   9  10  11  12
   2   4   6   8  10  12  14  16  18  20  22  24
   3   6   9  12  15  18  21  24  27  30  33  36
   4   8  12  16  20  24  28  32  36  40  44  48
   5  10  15  20  25  30  35  40  45  50  55  60
   6  12  18  24  30  36  42  48  54  60  66  72
   7  14  21  28  35  42  49  56  63  70  77  84
   8  16  24  32  40  48  56  64  72  80  88  96
   9  18  27  36  45  54  63  72  81  90  99 108
  10  20  30  40  50  60  70  80  90 100 110 120
  11  22  33  44  55  66  77  88  99 110 121 132
  12  24  36  48  60  72  84  96 108 120 132 144

Example 4:  Write a function that sums up integers from
a text file, one int per line.

Java:

    public static void sumFile ( String name ) {
        try {
            int total = 0;
            BufferedReader in = new BufferedReader ( new FileReader ( name ));
            for ( String s = in.readLine(); s != null; s = in.readLine() ) {
                total += Integer.parseInt ( s );
            }
            System.out.println ( total );
            in.close();
        }
        catch ( Exception xc ) {
            xc.printStackTrace();
        }
    }

Example 5:  Write function to print the odd numbers from 1 to 99.

C/C++:

    void printOdds() {
        for (int i = 1; i < 100; i += 2) {
            printf ("%d\n", i); // or cout << i << endl;
        }
    }

Java:

    public static void printOdds() {
        for (int i = 1; i < 100; i += 2) {
            System.out.println ( i );
        }
    }

Example 6:  Find the largest int value in an int array.

Java:

    public static int largest ( int[] input ) {
    int max = Integer.MIN_VALUE;
    for ( int i = 0; i < input.length; i++ ) {
        if ( input[i] > max ) max = input[i];
        }
        return max;
    }

Example 7:  Format an RGB value (three 1-byte
numbers) as a 6-digit hexadecimal string.

Java:

    public String formatRGB ( int r, int g, int b ) {
        return (toHex(r) + toHex(g) + toHex(b)).toUpperCase();
    }

    public String toHex ( int c ) {
        String s = Integer.toHexString ( c );
        return ( s.length() == 1 ) ? "0" + s : s;
    }

Or in Java 1.5:

    public String formatRGB ( int r, int g, int b ) {
        return String.format ( "%02X%02X%02X", r, g, b );
    }

Example output for (255, 0, 128):  

Few Software Development Knowledge

 What are the benefits of OOD?
o Object oriented design facilitates “Reusability”, “Extensibility” and “Modularity” of the software. We can divide the software into many components/classes so that “Abstraction” can be done on the changing part and non changing part to support the “changeability”. Plus Inheritance, Composition and polymorphism will always help in implementation.


 Explain how the Garbage Collector works in C#
o The GC of the C# (.Net rather) is a cool component in .NET framework. Being a C++ programmer, I truly understand the importance of it. I don’t need to worry about allocating /freeing the memory once I use it in .net.
In c#, all the object memory management is done in “Managed heap. GC collects the unused memory based on metadata information which gives the memory layout of the created object. It performs the collection in two phases.

Mark -> GC first finds the root of each object and traverse to the bottom of it adding each object and make a graph of it. It does not add the object already in the graph. The object not in a graph considered as a garbage.


Compact -> in this step, GC pushes the entire live object down to the heap re-arranging the pointers and making the free space on the top of the heap. It corrects the pointers in moving the object here and there.

What's the difference between Dispose and Finalize?
o Dispose and Finalize are both to remove the unmanaged memory allocated by the object. Dispose is an explicit way and programmers need to implement Idisposable interface where as finalize is the implicit way to free the memory and called by GC. Developer is not supposed to call the finalize method on an object but he/she can call dispose method. Microsoft recommends that we implement both Dispose and Finalize when working with unmanaged resources. The correct sequence then would be for a developer to call Dispose. The Finalize implementation would run and the resources would still be released when the object is garbage collected even if a developer neglected to call the Dispose method explicitly.

 What are the drawbacks in using the String class in C#?
o String class in C# is immutable and new memory is created whenever value of it is changed. If we do some operations of String object, a new memory is created and value is copied over there. This is a major problem if we use the long/huge string and manipulate it in C# Program.


 How does StringBuilder improve on that?
o StringBuilder is a Mutable class and new memory is not referenced when it value gets changed.


 What is an abstract class and when would you use it.
o Abstact class is a class having at least one abstract method/property on it. Abstract class cannot be instantiated and is a base class for other classes. We cannot use “sealed” keyword on it to prevent other classes to inherit from it. It is used when Common methods are implemented in a base class but other methods/properties will be changed in child classes.


 Test a stapler, provide all the test cases
Requirement test:
Size (length, breadth and height) of it.
Color of it.
Weight of it.
Size of Pin in it.
Does it have stapler indicator?
What type of metal used to make it?
It is magnetic?
Functional test:
what happens if you put bigger stapler pin?
What happens when it is jammed?
How does it work when there is no pin? Does it produce sound? or indicator blinks?
Does it have a base?
Does it have a body?
Does it have a rear pivot?
What is the max depth it can be used.
What happens if the size of the pin is smaller or bigger?
Does it have a staple exit?
What happens if I staple materials other then paper?
Usability Test:
can blind person use it?
Can a person with one only one hand use it?
What is the age limit to use it?
Does it contain harmful materials?
How much different size of Staplers it can use?
Do you need manual to use it?
Mass testing
All the staplers are of the same size and same functionality?
Do they have same materials?
Stress Testing
What max temp it can bear?
What is the min temp its spring can bear or work?
How much pressure needed to break it ?
Does it break if it falls from my desk or from the running vehicle?
Performance Test:
. How many staples can be stapled in the stapler's use-full life?
How many staples can be stapled in a sec or a minute?

Rule Test:
Do you need license to use it?
Does it harmful to the minor?
Do you need to tell which country is it made?
Does it expiration date? (Note: this is funny)



 Test an API called FormatURL which takes as an input a http URL string and replaces all special characters eg: space with %20 etc.,
o Test cases:
FormatURL(http://www.yahoo.com?name=deepak%20dhakal)
FormatURL(http://www.yahoo.com?name=%20%7Bdeepakdhakal)
FormatURL(http://www.yahoo.com?name=%20%7Bdeepakdhakal%20%5D)
FormatURL(http://www.yahoo.com?name=%21%7Bdeepakdhakal%20%5D) //non existence code
FormatURL(http://www.yahoo.com?name=%20)
FormatURL(“”)
FormatURL(“%7D”)
FormatURL(“%AAAA”)
FormatURL(%%%)
FormatURL(http://www.yahoo.com? %%%)
FormatURL(http://www.yahoo.com)