C++ Aptitude Questions and Answers

Posted by Stephen thangaraj at 02:10
C++ Aptitude Questions and Answers
1.Find the output of the following program
 class Sample
         int *ptr;
         Sample(int i)
         ptr = new int(i);
         delete ptr;
         void PrintVal()
         cout << "The value is " << *ptr;
 void SomeFunc(Sample x)
 cout << "Say i am in someFunc " << endl;
 int main()
 Sample s1= 10;

 Say i am in someFunc
 Null pointer assignment(Run-time error)

 As the object is passed by value to SomeFunc  the destructor of the object is called when the control returns from the function. So when PrintVal is called it meets up with ptr  that has been freed.The solution is to pass the Sample object  by reference to SomeFunc:

 void SomeFunc(Sample &x)
 cout << "Say i am in someFunc " << endl;
 because when we pass objects by refernece that object is not destroyed. while returning from the function.

2.Which is the parameter that is added to every non-static member function when it is called?
             ‘this’ pointer

3.Find the output of the following program
 class base
         int bval;
         base(){ bval=0;}

 class deri:public base
         int dval;
         deri(){ dval=1;}
 void SomeFunc(base *arr,int size)
 for(int i=0; i        cout<bval;

 int main()
 base BaseArr[5];
deri DeriArr[5];


 The function SomeFunc expects two arguments.The first one is a pointer to an array of base class objects and the second one is the sizeof the array.The first call of someFunc calls it with an array of bae objects, so it works correctly and prints the bval of all the objects. When Somefunc is called the second time the argument passed is the pointeer to an array of derived class objects and not the array of base class objects. But that is what the function expects to be sent. So the derived class pointer is promoted to base class pointer and the address is sent to the function. SomeFunc() knows nothing about this and just treats the pointer as an array of base class objects. So when arr++ is met, the size of base class object is taken into consideration and is incremented by sizeof(int) bytes for bval (the deri class objects have bval and dval as members and so is of size >= sizeof(int)+sizeof(int) ).

4.Find the output of the following program
 class base
             void baseFun(){ cout<<"from base"<        };
  class deri:public base
             void baseFun(){ cout<< "from derived"<        };
 void SomeFunc(base *baseObj)
 int main()
 base baseObject;
deri deriObject;

             from base
             from base

             As we have seen in the previous case, SomeFunc expects a pointer to a base class. Since a pointer to a derived class object is passed, it treats the argument only as a base class pointer and the corresponding base function is called.

5.Find the output of the following program
 class base
             virtual void baseFun(){ cout<<"from base"<        };
  class deri:public base
             void baseFun(){ cout<< "from derived"<        };
 void SomeFunc(base *baseObj)
 int main()
 base baseObject;
deri deriObject;

             from base
             from derived

             Remember that baseFunc is a virtual function. That means that it supports run-time polymorphism. So the function corresponding to the derived class object is called.
6.Base class has some virtual method and derived class has a method with the same name. If we initialize the base class pointer with derived object, calling of that virtual method will result in which method being called? 
a. Base method
b. Derived method..

 Ans. b

7.For the following C program
 #define AREA(x)(3.14*x*x)
 {float r1=6.25,r2=2.5,a;
 printf("\n Area of the circle is %f", a);
 printf("\n Area of the circle is %f", a);
 What is the output?

 Ans. Area of the circle is 122.656250
         Area of the circle is  19.625000

8.void main()
 int d=5;

 Ans: Undefined

9.void main()
 int i;
 case 1: printf("%d",i);break;
 case 2:printf("%d",i);break;
 case 3:printf("%d",i);break;
 switch(i) case 4:printf("%d",i);

 Ans: 1,2,3,4

10.void main()
 char *s="\12345s\n";

 Ans: 6

11.void main()
 unsigned i=1; /* unsigned char k= -1 => k=255; */
 signed j=-1; /* char k= -1 => k=65535 */
 /* unsigned or signed int k= -1 =>k=65535 */

 Ans: less

12.void main()
 float j;

 1. 1000000
 2. Overflow
 3. Error
 4. None

 Ans: 4

13.How do you declare an array of N pointers to functions returning  pointers to functions returning pointers to characters?

 Ans: The first part of this question can be answered in at least
         three ways:

     1. char *(*(*a[N])())();

     2. Build the declaration up incrementally, using typedefs:

         typedef char *pc;    /* pointer to char */
         typedef pc fpc();    /* function returning pointer to char */
         typedef fpc *pfpc;    /* pointer to above */
         typedef pfpc fpfpc();    /* function returning... */
         typedef fpfpc *pfpfpc;    /* pointer to... */
         pfpfpc a[N];         /* array of... */

     3. Use the cdecl program, which turns English into C and vice

         cdecl> declare a as array of pointer to function returning
             pointer to function returning pointer to char
         char *(*(*a[])())()

     cdecl can also explain complicated declarations, help with
     casts, and indicate which set of parentheses the arguments
     go in (for complicated function definitions, like the one
     Any good book on C should explain how to read these complicated
     C declarations "inside out" to understand them ("declaration
     mimics use").
     The pointer-to-function declarations in the examples above have
     not included parameter type information. When the parameters
     have complicated types, declarations can *really* get messy.
     (Modern versions of cdecl can help here, too.)
14.What is C++?

Released in 1985, C++ is an object-oriented programming language created by Bjarne Stroustrup. C++ maintains almost all aspects of the C language, while simplifying memory management and adding several features - including a new datatype known as a class (you will learn more about these later) - to allow object-oriented programming. C++ maintains the features of C which allowed for low-level memory access but also gives the programmer new tools to simplify memory management.

 C++ used for:

 C++ is a powerful general-purpose programming language. It can be used to create small programs or large applications. It can be used to make CGI scripts or console-only DOS programs. C++ allows you to create programs to do almost anything you need to do. The creator of C++, Bjarne Stroustrup, has put together a partial list of applications written in C++.

15.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.

16.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.

17.What is function overloading and operator overloading?

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).

18.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 << endl; }

19.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.

20.How do you write a function that can reverse a linked-list?

 void reverselist(void)
 head->next = 0;
 tail->next = head;
 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;

21.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.

22.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<MAX; i++) {
 cout << "Please enter your input between 5 and 9: ";
 cin >> numb;
 while ( numb<5 || numb>9) {
 cout << "Invalid input, please re-enter: ";
 cin >> numb;
 total = total + numb;
 average = total/MAX;
 cout << "The average number is: " << average << "\n";
 return 0;

23.Write a short code using C++ to print out all odd number from 1 to 100 using a for loop
 for( unsigned int i = 1; i < = 100; i++ )
 if( i & 0x00000001 )
 cout << i << \",\";

24.What is public, protected, private?
Public, protected and private are three access specifier in C++.
 Public data members and member functions are accessible outside the class.
 Protected data members and member functions are only available to derived classes.
 Private data members and member functions can’t be accessed outside the class. However there is an exception can be using friend classes.
 25.Write a function that swaps the values of two integers, using int* as the argument type.
 void swap(int* a, int*b) {
 int t;
 t = *a;
 *a = *b;
 *b = t;

Tell how to check whether a linked list is circular.
 Create two pointers, each set to the start of the list. Update each as follows:

while (pointer1) {
 pointer1 = pointer1->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.

26.What is virtual constructors/destructors?
 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.

 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?

27.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.

28.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<<endl; }

C++ Interview Questions and Answers

29.What is the difference between an ARRAY and a LIST?
 Array is collection of homogeneous elements.
 List is collection of heterogeneous elements.

 For Array memory allocated is static and continuous.
 For List memory allocated is dynamic and Random.

 Array: User need not have to keep in track of next memory allocation.
 List: User has to keep in Track of next location where memory is allocated.

 Array uses direct access of stored members, list uses sequencial access for members.

 //With Array you have direct access to memory position 5
 Object x = a[5]; // x takes directly a reference to 5th element of array

 //With the list you have to cross all previous nodes in order to get the 5th node:
 list mylist;
 list::iterator it;

 for( it = list.begin() ; it != list.end() ; it++ )
 if( i==5)
 x = *it;

30.Does c++ support multilevel and multiple inheritance?

31.What is a template?
 Templates allow to create generic functions that admit any data type as parameters and return value without having to overload the function with all the possible data types. Until certain point they fulfill the functionality of a macro. Its prototype is any of the two following ones:

 template <class indetifier> function_declaration; template <typename indetifier> 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.

32.Define a constructor - What it is and how it might be called (2 methods).
 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.

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


 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().
 33.Explain differences between eg. new() and malloc()
 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()]

 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.

34.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.

35.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.

36.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

 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

 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
 SHAPE *newShape;

 37.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(){

 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.

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

39.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.

40.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.

41.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

42.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.

43.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;

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

44.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

45.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.

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

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

48.What are 2 ways of exporting a function from a DLL?
1.Taking a reference to the function from the DLL instance.
 2. Using the DLL ’s Type Library

49.What is the difference between an object and a class?
 Classes and objects are separate but related concepts. Every object belongs to a class and every class contains one or more related objects.
 - A Class is static. All of the attributes of a class are fixed before, during, and after the execution of a program. The attributes of a class don't change.
 - The class to which an object belongs is also (usually) static. If a particular object belongs to a certain class at the time that it is created then it almost certainly will still belong to that class right up until the time that it is destroyed.
 - An Object on the other hand has a limited lifespan. Objects are created and eventually destroyed. Also during that lifetime, the attributes of the object may undergo significant change.

Suppose that data is an array of 1000 integers. Write a single function call that will sort the 100 elements data [222] through data [321].
 quicksort ((data + 222), 100);

50.What is a class?
 Class is a user-defined data type in C++. It can be created to solve a particular kind of problem. After creation the user need not know the specifics of the working of a class.

51.What is friend function?
 As the name suggests, the function acts as a friend to a class. As a friend of a class, it can access its private and protected members. A friend function is not a member of the class. But it must be listed in the class definition.

52.Which recursive sorting technique always makes recursive calls to sort subarrays that are about half size of the original array?
 Mergesort always makes recursive calls to sort subarrays that are about half size of the original array, resulting in O(n log n) time.

53.What is abstraction?
 Abstraction is of the process of hiding unwanted details from the user.

54.What are virtual functions?
 A virtual function allows derived classes to replace the implementation provided by the base class. The compiler makes sure the replacement is always called whenever the object in question is actually of the derived class, even if the object is accessed by a base pointer rather than a derived pointer. This allows algorithms in the base class to be replaced in the derived class, even if users don't know about the derived class.

55.What is the difference between an external iterator and an internal iterator? Describe an advantage of an external iterator.
 An internal iterator is implemented with member functions of the class that has items to step through. .An external iterator is implemented as a separate class that can be "attach" to the object that has items to step through. .An external iterator has the advantage that many difference iterators can be active simultaneously on the same object.

56.What is a scope resolution operator?
 A scope resolution operator (::), can be used to define the member functions of a class outside the class.

57.What do you mean by pure virtual functions?
 A pure virtual member function is a member function that the base class forces derived classes to provide. Normally these member functions have no implementation. Pure virtual functions are equated to zero.
 class Shape { public: virtual void draw() = 0; };

58.What is polymorphism? Explain with an example?
 "Poly" means "many" and "morph" means "form". Polymorphism is the ability of an object (or reference) to assume (be replaced by) or become many different forms of object.
 Example: function overloading, function overriding, virtual functions. Another example can be a plus ‘+’ sign, used for adding two integers or for using it to concatenate two strings.

#include <stdio.h>
 typedef union
 int a;
 char b[10];
 float c;

 Union x,y = {100};
 x.a = 50;
 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)

60.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.

61.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.

62.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.

63.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.

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

65.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.

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

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

67.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.

68.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.

69.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.

70.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.

71.What’s the auto keyword good for?
 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;”

 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.

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

 The difference is this:
 p is pointing to a constant string, you can never safely say
 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.)

 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).

 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)……

73.How do I declare an array of N pointers to functions returning pointers to functions returning pointers to characters?
 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

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

74.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.

75.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);


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

77.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.

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

79.How many ways are there to initialize an int with a constant?
 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);

80.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.

81.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; }

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

83.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.

84.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."

85.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.

86.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.

87.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.

88.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.

89.What is the Standard Template Library (STL)?
A library of container templates approved by the ANSI committee for inclusion in the standard C++ specification.
 A programmer who then launches into a discussion of the generic programming model, iterators, allocators, algorithms, and such, has a higher than average understanding of the new technology that STL brings to C++ programming.

90.Describe run-time type identification.
 The ability to determine at run time the type of an object by using the typeid operator or the dynamic_cast operator.

91.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.
 This solution assumes that two library vendors don’t use the same namespace identifier, of course.

92.Are there any new intrinsic (built-in) data types?
 Yes. The ANSI committee added the bool intrinsic type and its true and false value keywords.

93.Will the following program execute?
 void main()
{ void *vptr = (void *) malloc(sizeof(void));

 It will throw an error, as arithmetic operations cannot be performed on void pointers.

 It will not build as sizeof cannot be applied to void* ( error “Unknown size” )

 How can it execute if it won’t even compile? It needs to be int main, not void main. Also, cannot increment a void *.

 According to gcc compiler it won’t show any error, simply it executes. but in general we can’t do arthematic operation on void, and gives size of void as 1

 The program compiles in GNU C while giving a warning for “void main”. The program runs without a crash. sizeof(void) is “1? hence when vptr++, the address is incremented by 1.

 Regarding arguments about GCC, be aware that this is a C++ question, not C. So gcc will compile and execute, g++ cannot. g++ complains that the return type cannot be void and the argument of sizeof() cannot be void. It also reports that ISO C++ forbids incrementing a pointer of type ‘void*’.

 in C++
 voidp.c: In function `int main()’:
 voidp.c:4: error: invalid application of `sizeof’ to a void type
 voidp.c:4: error: `malloc’ undeclared (first use this function)
 voidp.c:4: error: (Each undeclared identifier is reported only once for each function it appears in.)
 voidp.c:6: error: ISO C++ forbids incrementing a pointer of type `void*’

 But in c, it work without problems

void main()
 char *cptr = 0?2000;
 long *lptr = 0?2000;
 printf(” %x %x”, cptr, lptr);
 Will it execute or not?
 For Q2: As above, won’t compile because main must return int. Also, 0×2000 cannot be implicitly converted to a pointer (I assume you meant 0×2000 and not 0?2000.)

 Not Excute.
 Compile with VC7 results following errors:
 error C2440: ‘initializing’ : cannot convert from ‘int’ to ‘char *’
 error C2440: ‘initializing’ : cannot convert from ‘int’ to ‘long *’

 Not Excute if it is C++, but Excute in C.
 The printout:
 2001 2004

 In C++
 [$]> g++ point.c
 point.c: In function `int main()’:
 point.c:4: error: invalid conversion from `int’ to `char*’
 point.c:5: error: invalid conversion from `int’ to `long int*’

 in C
 [$] etc > gcc point.c
 point.c: In function `main’:
 point.c:4: warning: initialization makes pointer from integer without a cast
 point.c:5: warning: initialization makes pointer from integer without a cast
 [$] etc > ./a.exe
 2001 2004

94.What is the difference between Mutex and Binary semaphore?
semaphore is used to synchronize processes. where as mutex is used to provide synchronization between threads running in the same process.

95.In C++, what is the difference between method overloading and method overriding?
 Overloading a method (or function) in C++ is the ability for functions of the same name to be defined as long as these methods have different signatures (different set of parameters). Method overriding is the ability of the inherited class rewriting the virtual method of the base class.

96.What methods can be overridden in Java?
 In C++ terminology, all public methods in Java are virtual. Therefore, all Java methods can be overwritten in subclasses except those that are declared final, static, and private.

97.What are the defining traits of an object-oriented language?
 The defining traits of an object-oriented langauge are:
 * encapsulation
 * inheritance
 * polymorphism

98.Write a program that ask for user input from 5 to 9 then calculate the average
 int main()
 int MAX=4;
 int total =0;
 int average=0;
 int numb;
 cout<<"Please enter your input from 5 to 9";
 if((numb <5)&&(numb>9))
 cout<<"please re type your input";
 for(i=0;i<=MAX; i++)
 total = total + numb;
 average= total /MAX;
 cout<<"The average number is"<<average<<endl;

 return 0;

99.Assignment Operator - What is the diffrence between a "assignment operator" and a "copy constructor"?
 In assignment operator, you are assigning a value to an existing object. But in copy constructor, you are creating a new object and then assigning a value to that object. For example:
 complex c1,c2;
 c1=c2; //this is assignment
 complex c3=c2; //copy constructor

 A copy constructor is used to initialize a newly declared variable from an existing variable. This makes a deep copy like assignment, but it is somewhat simpler:

 There is no need to test to see if it is being initialized from itself.
 There is no need to clean up (eg, delete) an existing value (there is none).
 A reference to itself is not returned.

RTTI - What is RTTI?
 RTTI stands for "Run Time Type Identification". In an inheritance hierarchy, we can find out the exact type of the objet of which it is member. It can be done by using:

 1) dynamic id operator
 2) typecast operator

 RTTI is defined as follows: Run Time Type Information, a facility that allows an object to be queried at runtime to determine its type. One of the fundamental principles of object technology is polymorphism, which is the ability of an object to dynamically change at runtime.

100.STL Containers - What are the types of STL containers?
 There are 3 types of STL containers:

 1. Adaptive containers like queue, stack
 2. Associative containers like set, map
 3. Sequence containers like vector, deque

101. What is slicing?
 Slicing means that the data added by a subclass are discarded when an object of the subclass is passed or returned by value or from a function expecting a base class object.    
 Consider the following class declaration:
                class base
                      base& operator =(const base&);
                      base (const base&);
               void fun( )
                     base e=m;
 As base copy functions don't know anything about the derived only the base part of the derived is copied. This is commonly referred to as slicing. One reason to pass objects of classes in a hierarchy is to avoid slicing. Other reasons are to preserve polymorphic behavior and to gain efficiency.

102.What is name mangling?
 Name mangling is the process through which your c++ compilers give each function in your program a unique name. In C++, all programs have at-least a few functions with the same name. Name mangling is a concession to the fact that linker always insists on all function names being unique.
             In general, member names are made unique by concatenating the name of the member with that of the class e.g. given the declaration:
     class Bar
                 int ival;
 ival becomes something like:
       // a possible member name mangling
 Consider this derivation:
      class Foo : public Bar
               int ival;
 The internal representation of a Foo object is the concatenation of its base and derived class members.
      // Pseudo C++ code
     // Internal representation of Foo
     class Foo
              int ival__3Bar;
              int ival__3Foo;
 Unambiguous access of either ival members is achieved through name mangling. Member functions, because they can be overloaded, require an extensive mangling to provide each with a unique name. Here the compiler generates the same name for the two overloaded instances(Their argument lists make their instances unique).  

103.What are proxy objects?
 Objects that points to other objects are called proxy objects or surrogates. Its an object that provides the same interface as its server object but does not have any functionality. During a method invocation, it routes data to the true server object and sends back the return value to the object.

104.Differentiate between declaration and definition in C++.
 A declaration introduces a name into the program; a definition provides a unique description of an entity (e.g. type, instance, and function). Declarations can be repeated in a given scope, it introduces a name in a given scope. There must be exactly one definition of every object, function or class used in a C++ program.
 A declaration is a definition unless:
 Ø  it declares a function without specifying its body,
 Ø  it contains an extern specifier and no initializer or function body,
 Ø  it is the declaration of a static class data member without a class definition,
 Ø  it is a class name definition,
 Ø  it is a typedef declaration.
             A definition is a declaration unless:
 Ø  it defines a static class data member,
 Ø  it defines a non-inline member function.

105.What is cloning?
 An object can carry out copying in two ways i.e. it can set itself to be a copy of another object, or it can return a copy of itself. The latter process is called cloning.

Describe the main characteristics of static functions.
 The main characteristics of static functions include,
 Ø  It is without the a this pointer,
 Ø  It can't directly access the non-static members of its class
 Ø  It can't be declared const, volatile or virtual.
 Ø  It doesn't need to be invoked through an object of its class, although for convenience, it may.             

106.Will the inline function be compiled as the inline function always? Justify.
 An inline function is a request and not a command. Hence it won't be compiled as an inline function always.
             Inline-expansion could fail if the inline function contains loops, the address of an inline function is used, or an inline function is called in a complex expression. The rules for inlining are compiler dependent.

107.Define a way other than using the keyword inline to make a function inline.
 The function must be defined inside the class.  

108.How can a '::' operator be used as unary operator?
 The scope operator can be used to refer to members of the global namespace. Because the global namespace doesn’t have a name, the notation :: member-name refers to a member of the global namespace. This can be useful for referring to members of global namespace whose names have been hidden by names declared in nested local scope. Unless we specify to the compiler in which namespace to search for a declaration, the compiler simple searches the current scope, and any scopes in which the current scope is nested, to find the declaration for the name.

109.What is placement new?
 When you want to call a constructor directly, you use the placement new. Sometimes you have some raw memory that's already been allocated, and you need to construct an object in the memory you have. Operator new's special version placement new allows you to do it.
            class Widget
                public :
                      Widget(int widgetsize);
                       Widget* Construct_widget_int_buffer(void *buffer,int widgetsize)
                               return new(buffer) Widget(widgetsize);
             This function returns a pointer to a Widget object that's constructed within the buffer passed to the function. Such a function might be useful for applications using shared memory or memory-mapped I/O, because objects in such applications must be placed at specific addresses or in memory allocated by special routines.

 110.What do you mean by analysis and design?
 Basically, it is the process of determining what needs to be done before how it should be done. In order to accomplish this, the developer refers the existing systems and documents. So, simply it is an art of discovery.
 It is the process of adopting/choosing the one among the many, which best accomplishes the users needs. So, simply, it is compromising mechanism.

111.What are the steps involved in designing?
 Before getting into the design the designer should go through the SRS prepared by the System Analyst.
             The main tasks of design are Architectural Design and Detailed Design.
             In Architectural Design we find what are the main modules in the problem domain.
 In Detailed Design we find what should be done within each module.

112.What are the main underlying concepts of object orientation?
 Objects, messages, class, inheritance and polymorphism are the main concepts of object orientation.

113.What do u meant by "SBI" of an object?
 SBI stands for State, Behavior and Identity. Since every object has the above three.
 Ø  State:        
 It is just a value to the attribute of an object at a particular time.
 Ø  Behaviour:
 It describes the actions and their reactions of that object.
 Ø  Identity:
 An object has an identity that characterizes its own existence. The identity makes it possible to distinguish any object in an unambiguous way, and independently from its state.

114.Differentiate persistent & non-persistent objects?
 Persistent refers to an object's ability to transcend time or space. A persistent object stores/saves its state in a permanent storage system with out losing the information represented by the object.
 A non-persistent object is said to be transient or ephemeral. By default objects are considered as non-persistent.

115.What do you meant by active and passive objects?
 Active objects are one which instigate an interaction which owns a thread and they are responsible for handling control to other objects. In simple words it can be referred as client.
 Passive objects are one, which passively waits for the message to be processed. It waits for another object that requires its services. In simple words it can be referred as server.

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