MFC Interview Question Part2

How do you find out if a linked-list has an end? (i.e. the list is not a cycle)

You can find out by using 2 pointers. One of them goes 2 nodes each time. The second one goes at 1 nodes each time. If there is a cycle, the one that goes 2 nodes each time will eventually meet the one that goes slower. If that is the case, then you will know the linked-list is a cycle.


What is the difference between realloc() and free()?

The free subroutine frees a block of memory previously allocated by the malloc subroutine. Undefined results occur if the Pointer parameter is not a valid pointer. If the Pointer parameter is a null value, no action will occur. The realloc subroutine changes the size of the block of memory pointed to by the Pointer parameter to the number of bytes specified by the Size parameter and returns a new pointer to the block. The pointer specified by the Pointer parameter must have been created with the malloc, calloc, or realloc subroutines and not been deallocated with the free or realloc subroutines. Undefined results occur if the Pointer parameter is not a valid pointer.

What is function overloading and operator overloading?


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Function overloading: C++ enables several functions of the same name to be defined, as long as these functions have different sets of parameters (at least as far as their types are concerned). This capability is called function overloading. When an overloaded function is called, the C++ compiler selects the proper function by examining the number, types and order of the arguments in the call. Function overloading is commonly used to create several functions of the same name that perform similar tasks but on different data types.
Operator overloading allows existing C++ operators to be redefined so that they work on objects of user-defined classes. Overloaded operators are syntactic sugar for equivalent function calls. They form a pleasant facade that doesn't add anything fundamental to the language (but they can improve understandability and reduce maintenance costs).

What is the difference between declaration and definition?

The declaration tells the compiler that at some later point we plan to present the definition of this declaration.
E.g.: void stars () //function declaration
The definition contains the actual implementation.
E.g.: void stars () // declarator
{
for(int j=10; j > =0; j--) //function body
cout << *; cout << head="="0)">next==0)
return;
if(head->next==tail)
{
head->next = 0;
tail->next = head;
}
else
{
node* pre = head;
node* cur = head->next;
node* curnext = cur->next;
head->next = 0;
cur-> next = head;

for(; curnext!=0; )
{
cur->next = pre;
pre = cur;
cur = curnext;
curnext = curnext->next;
}

curnext->next = cur;
}




What is virtual constructors/destructors?
Answer1
Virtual destructors:
If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base-class destructor function (matching the pointer type) is called on the object.
There is a simple solution to this problem declare a virtual base-class destructor.
This makes all derived-class destructors virtual even though they don’t have the same name as the base-class destructor. Now, if the object in the hierarchy is destroyed explicitly by applying the delete operator to a base-class pointer to a derived-class object, the destructor for the appropriate class is called. Virtual constructor: Constructors cannot be virtual. Declaring a constructor as a virtual function is a syntax error.

Answer2
Virtual destructors: If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base-class destructor function (matching the pointer type) is called on the object.
There is a simple solution to this problem – declare a virtual base-class destructor. This makes all derived-class destructors virtual even though they don’t have the same name as the base-class destructor. Now, if the object in the hierarchy is destroyed explicitly by applying the delete operator to a base-class pointer to a derived-class object, the destructor for the appropriate class is called.

Virtual constructor: Constructors cannot be virtual. Declaring a constructor as a virtual function is a syntax error. Does c++ support multilevel and multiple inheritance?
Yes.

What are the advantages of inheritance?
• It permits code reusability.
• Reusability saves time in program development.
• It encourages the reuse of proven and debugged high-quality software, thus reducing problem after a system becomes functional.

What is the difference between declaration and definition?
The declaration tells the compiler that at some later point we plan to present the definition of this declaration.
E.g.: void stars () //function declaration
The definition contains the actual implementation.
E.g.: void stars () // declarator
{
for(int j=10; j>=0; j--) //function body
cout<<”*”; cout<next;
pointer2 = pointer2->next; if (pointer2) pointer2=pointer2->next;
if (pointer1 == pointer2) {
print (\"circular\n\");
}
}

OK, why does this work?
If a list is circular, at some point pointer2 will wrap around and be either at the item just before pointer1, or the item before that. Either way, it’s either 1 or 2 jumps until they meet.






What do you mean by inline function?
The idea behind inline functions is to insert the code of a called function at the point where the function is called. If done carefully, this can improve the application's performance in exchange for increased compile time and possibly (but not always) an increase in the size of the generated binary executables.

Write a program that ask for user input from 5 to 9 then calculate the average
#include "iostream.h"
int main() {
int MAX = 4;
int total = 0;
int average;
int numb;
for (int i=0; i> numb;
while ( numb<5>9) {
cout << "Invalid input, please re-enter: "; cin >> numb;
}
total = total + numb;
}
average = total/MAX;
cout << "The average number is: " << i =" 1;" t =" *a;" a =" *b;" b =" t;" x =" a[5];" it =" list.begin()" i="="5)" x =" *it;">function_declaration; template function_declaration;
The only difference between both prototypes is the use of keyword class or typename, its use is indistinct since both expressions have exactly the same meaning and behave exactly the same way.

Define a constructor - What it is and how it might be called (2 methods).
Answer1
constructor is a member function of the class, with the name of the function being the same as the class name. It also specifies how the object should be initialized.

Ways of calling constructor:
1) Implicitly: automatically by complier when an object is created.
2) Calling the constructors explicitly is possible, but it makes the code unverifiable.

Answer2
class Point2D{
int x; int y;
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
};

main(){

Point2D MyPoint; // Implicit Constructor call. In order to allocate memory on stack, the default constructor is implicitly called.

Point2D * pPoint = new Point2D(); // Explicit Constructor call. In order to allocate memory on HEAP we call the default constructor.

You have two pairs: new() and delete() and another pair : alloc() and free().
Explain differences between eg. new() and malloc()
Answer1
1.) “new and delete” are preprocessors while “malloc() and free()” are functions. [we dont use brackets will calling new or delete].
2.) no need of allocate the memory while using “new” but in “malloc()” we have to use “sizeof()”.
3.) “new” will initlize the new memory to 0 but “malloc()” gives random value in the new alloted memory location [better to use calloc()]

Answer2
new() allocates continous space for the object instace
malloc() allocates distributed space.
new() is castless, meaning that allocates memory for this specific type,
malloc(), calloc() allocate space for void * that is cated to the specific class type pointer.

What is the difference between class and structure?
Structure: Initially (in C) a structure was used to bundle different type of data types together to perform a particular functionality. But C++ extended the structure to contain functions also. The major difference is that all declarations inside a structure are by default public.
Class: Class is a successor of Structure. By default all the members inside the class are private.



What is RTTI?
Runtime type identification (RTTI) lets you find the dynamic type of an object when you have only a pointer or a reference to the base type. RTTI is the official way in standard C++ to discover the type of an object and to convert the type of a pointer or reference (that is, dynamic typing). The need came from practical experience with C++. RTTI replaces many Interview Questions - Homegrown versions with a solid, consistent approach.

What is encapsulation?
Packaging an object’s variables within its methods is called encapsulation.

Explain term POLIMORPHISM and give an example using eg. SHAPE object: If I have a base class SHAPE, how would I define DRAW methods for two objects CIRCLE and SQUARE

Answer1
POLYMORPHISM : A phenomenon which enables an object to react differently to the same function call.
in C++ it is attained by using a keyword virtual

Example
public class SHAPE
{
public virtual void SHAPE::DRAW()=0;
}
Note here the function DRAW() is pure virtual which means the sub classes must implement the DRAW() method and SHAPE cannot be instatiated

public class CIRCLE::public SHAPE
{
public void CIRCLE::DRAW()
{
// TODO drawing circle
}
}
public class SQUARE::public SHAPE
{
public void SQUARE::DRAW()
{
// TODO drawing square
}
}
now from the user class the calls would be like
globally
SHAPE *newShape;

When user action is to draw
public void MENU::OnClickDrawCircle(){
newShape = new CIRCLE();
}

public void MENU::OnClickDrawCircle(){
newShape = new SQUARE();

}

the when user actually draws
public void CANVAS::OnMouseOperations(){
newShape->DRAW();
}


Answer2
class SHAPE{
public virtual Draw() = 0; //abstract class with a pure virtual method
};

class CIRCLE{
public int r;
public virtual Draw() { this->drawCircle(0,0,r); }
};

class SQURE
public int a;
public virtual Draw() { this->drawRectangular(0,0,a,a); }
};

Each object is driven down from SHAPE implementing Draw() function in its own way.

What is an object?
Object is a software bundle of variables and related methods. Objects have state and behavior.

How can you tell what shell you are running on UNIX system?
You can do the Echo $RANDOM. It will return a undefined variable if you are from the C-Shell, just a return prompt if you are from the Bourne shell, and a 5 digit random numbers if you are from the Korn shell. You could also do a ps -l and look for the shell with the highest PID.

What do you mean by inheritance?
Inheritance is the process of creating new classes, called derived classes, from existing classes or base classes. The derived class inherits all the capabilities of the base class, but can add embellishments and refinements of its own







Describe PRIVATE, PROTECTED and PUBLIC – the differences and give examples.
class Point2D{
int x; int y;

public int color;
protected bool pinned;
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
};

Point2D MyPoint;

You cannot directly access private data members when they are declared (implicitly) private:

MyPoint.x = 5; // Compiler will issue a compile ERROR
//Nor yoy can see them:
int x_dim = MyPoint.x; // Compiler will issue a compile ERROR

On the other hand, you can assign and read the public data members:

MyPoint.color = 255; // no problem
int col = MyPoint.color; // no problem

With protected data members you can read them but not write them: MyPoint.pinned = true; // Compiler will issue a compile ERROR

bool isPinned = MyPoint.pinned; // no problem

What is namespace?
Namespaces allow us to group a set of global classes, objects and/or functions under a name. To say it somehow, they serve to split the global scope in sub-scopes known as namespaces.
The form to use namespaces is:
namespace identifier { namespace-body }
Where identifier is any valid identifier and namespace-body is the set of classes, objects and functions that are included within the namespace. For example:
namespace general { int a, b; } In this case, a and b are normal variables integrated within the general namespace. In order to access to these variables from outside the namespace we have to use the scope operator ::. For example, to access the previous variables we would have to put:
general::a general::b
The functionality of namespaces is specially useful in case that there is a possibility that a global object or function can have the same name than another one, causing a redefinition error.

What is a COPY CONSTRUCTOR and when is it called?
A copy constructor is a method that accepts an object of the same class and copies it’s data members to the object on the left part of assignement:

class Point2D{
int x; int y;

public int color;
protected bool pinned;
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
public Point2D( const Point2D & ) ;
};

Point2D::Point2D( const Point2D & p )
{
this->x = p.x;
this->y = p.y;
this->color = p.color;
this->pinned = p.pinned;
}

main(){
Point2D MyPoint;
MyPoint.color = 345;
Point2D AnotherPoint = Point2D( MyPoint ); // now AnotherPoint has color = 345


What is Boyce Codd Normal form?
A relation schema R is in BCNF with respect to a set F of functional dependencies if for all functional dependencies in F+ of the form a-> , where a and b is a subset of R, at least one of the following holds:
* a- > b is a trivial functional dependency (b is a subset of a)
* a is a superkey for schema R

What is virtual class and friend class?
Friend classes are used when two or more classes are designed to work together and need access to each other's implementation in ways that the rest of the world shouldn't be allowed to have. In other words, they help keep private things private. For instance, it may be desirable for class DatabaseCursor to have more privilege to the internals of class Database than main() has.

What is the word you will use when defining a function in base class to allow this function to be a polimorphic function?
virtual

What do you mean by binding of data and functions?
Encapsulation.





What’s the output of the following program? Why?
#include
main()
{
typedef union
{
int a;
char b[10];
float c;
}
Union;

Union x,y = {100};
x.a = 50;
strcpy(x.b,\"hello\");
x.c = 21.50;

printf(\"Union x : %d %s %f \n\",x.a,x.b,x.c );
printf(\"Union y :%d %s%f \n\",y.a,y.b,y.c);
}

Given inputs X, Y, Z and operations and & (meaning bitwise OR and AND, respectively)
What is output equal to in
output = (X & Y) (X & Z) (Y & Z)

Why are arrays usually processed with for loop?
The real power of arrays comes from their facility of using an index variable to traverse the array, accessing each element with the same expression a[i]. All the is needed to make this work is a iterated statement in which the variable i serves as a counter, incrementing from 0 to a.length -1. That is exactly what a loop does.

What is an HTML tag?
Answer: An HTML tag is a syntactical construct in the HTML language that abbreviates specific instructions to be executed when the HTML script is loaded into a Web browser. It is like a method in Java, a function in C++, a procedure in Pascal, or a subroutine in FORTRAN.

Explain which of the following declarations will compile and what will be constant - a pointer or the value pointed at: * const char *
* char const *
* char * const

Note: Ask the candidate whether the first declaration is pointing to a string or a single character. Both explanations are correct, but if he says that it’s a single character pointer, ask why a whole string is initialized as char* in C++. If he says this is a string declaration, ask him to declare a pointer to a single character. Competent candidates should not have problems pointing out why const char* can be both a character and a string declaration, incompetent ones will come up with invalid reasons.

You’re given a simple code for the class Bank Customer. Write the following functions:
* Copy constructor
* = operator overload
* == operator overload
* + operator overload (customers’ balances should be added up, as an example of joint account between husband and wife)

Note:Anyone confusing assignment and equality operators should be dismissed from the interview. The applicant might make a mistake of passing by value, not by reference. The candidate might also want to return a pointer, not a new object, from the addition operator. Slightly hint that you’d like the value to be changed outside the function, too, in the first case. Ask him whether the statement customer3 = customer1 + customer2 would work in the second case.

What problems might the following macro bring to the application?
#define sq(x) x*x

Anything wrong with this code?
T *p = new T[10];
delete p;

Everything is correct, Only the first element of the array will be deleted”, The entire array will be deleted, but only the first element destructor will be called.

Anything wrong with this code?
T *p = 0;
delete p;

Yes, the program will crash in an attempt to delete a null pointer.

How do you decide which integer type to use?
It depends on our requirement. When we are required an integer to be stored in 1 byte (means less than or equal to 255) we use short int, for 2 bytes we use int, for 8 bytes we use long int.

A char is for 1-byte integers, a short is for 2-byte integers, an int is generally a 2-byte or 4-byte integer (though not necessarily), a long is a 4-byte integer, and a long long is a 8-byte integer





What does extern mean in a function declaration?
Using extern in a function declaration we can make a function such that it can used outside the file in which it is defined.

An extern variable, function definition, or declaration also makes the described variable or function usable by the succeeding part of the current source file. This declaration does not replace the definition. The declaration is used to describe the variable that is externally defined.

If a declaration for an identifier already exists at file scope, any extern declaration of the same identifier found within a block refers to that same object. If no other declaration for the identifier exists at file scope, the identifier has external linkage.

What can I safely assume about the initial values of variables which are not explicitly initialized?
It depends on complier which may assign any garbage value to a variable if it is not initialized.

What is the difference between char a[] = “string”; and char *p = “string”;?
In the first case 6 bytes are allocated to the variable a which is fixed, where as in the second case if *p is assigned to some other value the allocate memory can change.

What’s the auto keyword good for?
Answer1
Not much. It declares an object with automatic storage duration. Which means the object will be destroyed at the end of the objects scope. All variables in functions that are not declared as static and not dynamically allocated have automatic storage duration by default.

For example
int main()
{
int a; //this is the same as writing “auto int a;”
}

Answer2
Local variables occur within a scope; they are “local” to a function. They are often called automatic variables because they automatically come into being when the scope is entered and automatically go away when the scope closes. The keyword auto makes this explicit, but local variables default to auto auto auto auto so it is never necessary to declare something as an auto auto auto auto.

What is the difference between char a[] = “string”; and char *p = “string”; ?
Answer1
a[] = “string”;
char *p = “string”;

The difference is this:
p is pointing to a constant string, you can never safely say
p[3]=’x';
however you can always say a[3]=’x';

char a[]=”string”; - character array initialization.
char *p=”string” ; - non-const pointer to a const-string.( this is permitted only in the case of char pointer in C++ to preserve backward compatibility with C.)

Answer2
a[] = “string”;
char *p = “string”;

a[] will have 7 bytes. However, p is only 4 bytes. P is pointing to an adress is either BSS or the data section (depending on which compiler — GNU for the former and CC for the latter).

Answer3
char a[] = “string”;
char *p = “string”;

for char a[]…….using the array notation 7 bytes of storage in the static memory block are taken up, one for each character and one for the terminating nul character.

But, in the pointer notation char *p………….the same 7 bytes required, plus N bytes to store the pointer variable “p” (where N depends on the system but is usually a minimum of 2 bytes and can be 4 or more)……

How do I declare an array of N pointers to functions returning pointers to functions returning pointers to characters?
Answer1
If you want the code to be even slightly readable, you will use typedefs.
typedef char* (*functiontype_one)(void);
typedef functiontype_one (*functiontype_two)(void);
functiontype_two myarray[N]; //assuming N is a const integral

Answer2
char* (* (*a[N])())()
Here a is that array. And according to question no function will not take any parameter value.

What does extern mean in a function declaration?
It tells the compiler that a variable or a function exists, even if the compiler hasn’t yet seen it in the file currently being compiled. This variable or function may be defined in another file or further down in the current file.





How do I initialize a pointer to a function?
This is the way to initialize a pointer to a function
void fun(int a)
{

}

void main()
{
void (*fp)(int);
fp=fun;
fp(1);

}

How do you link a C++ program to C functions?
By using the extern "C" linkage specification around the C function declarations.

Explain the scope resolution operator.
It permits a program to reference an identifier in the global scope that has been hidden by another identifier with the same name in the local scope.

What are the differences between a C++ struct and C++ class?
The default member and base-class access specifier are different.

How many ways are there to initialize an int with a constant?
Two.
There are two formats for initializers in C++ as shown in the example that follows. The first format uses the traditional C notation. The second format uses constructor notation.
int foo = 123;
int bar (123);

How does throwing and catching exceptions differ from using setjmp and longjmp?
The throw operation calls the destructors for automatic objects instantiated since entry to the try block.

What is a default constructor?
Default constructor WITH arguments class B { public: B (int m = 0) : n (m) {} int n; }; int main(int argc, char *argv[]) { B b; return 0; }

What is a conversion constructor?
A constructor that accepts one argument of a different type.

What is the difference between a copy constructor and an overloaded assignment operator?
A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.

When should you use multiple inheritance?
There are three acceptable answers: "Never," "Rarely," and "When the problem domain cannot be accurately modeled any other way."

Explain the ISA and HASA class relationships. How would you implement each in a class design?
A specialized class "is" a specialization of another class and, therefore, has the ISA relationship with the other class. An Employee ISA Person. This relationship is best implemented with inheritance. Employee is derived from Person. A class may have an instance of another class. For example, an employee "has" a salary, therefore the Employee class has the HASA relationship with the Salary class. This relationship is best implemented by embedding an object of the Salary class in the Employee class.

When is a template a better solution than a base class?
When you are designing a generic class to contain or otherwise manage objects of other types, when the format and behavior of those other types are unimportant to their containment or management, and particularly when those other types are unknown (thus, the generosity) to the designer of the container or manager class.

What is a mutable member?
One that can be modified by the class even when the object of the class or the member function doing the modification is const.

What is an explicit constructor?
A conversion constructor declared with the explicit keyword. The compiler does not use an explicit constructor to implement an implied conversion of types. It’s purpose is reserved explicitly for construction