CPP FOR UR INTERVIEW

C And C++
i=23, j=4, c=0;
c=i++-++j;
o/p?
#define CUBE(x) x*x*x
#define MUL3(x,y) 3*x*y
#define ADD(x) x+y
some statement maikng use of the preprocessors defined above…………find o/p.
virtual destructors r used for ?
2 questions on friend functions & classes
char c[]=”123456789″;
i=4;
printf(”%c %c”, c[i], i[c]);
o/p?
one more question on these lines.
int *ptr;
p=0;
p++;
printf(”%u”, p);
o/p?
a. 0 b. garbage value c. 4 d. none of the above
double i=0.0;
switch(i)
{
case 0.0:
printf(”jgdj”);
case 1.0:
printf(”ptoy”);
break;
default:
printf(”hdfv”);
}
o/p?
volatile int i;
in d above statement, is “volatile”
a. a type declaration b. type qualifier c. storage class d. none of the above
Unix
“bash” is a kind of shell in UNIX
primitive flavours of unix
options : a. BSD &Sys V b. LINUX & BSD c..
which of the folllowing is used 4 redirection in UNIX? >, |, <, ^ wot is d UNIX terminology 4 multi-tasking? a. time slicing b. pre-emptive ……. c. time division d……. In UNIX if You try accessing a directory for which u dont have permission, wot message is displayed? a. permission denied b. invalid user c. access denied d……… cpp programs and aswers By admin on April 28th, 2008 21. Differentiate the following notations? I: :obj1 :obj2 II: :obj1 :obj2 In the above representation I, obj1 sends message to obj2. But in the case of II the data is transferred from obj1 to obj2. 22. USECASE is an implementation independent notation. How will the designer give the implementation details of a particular USECASE to the programmer? This can be accomplished by specifying the relationship called “refinement” which talks about the two different abstraction of the same thing. Or example, calculate pay calculate class1 class2 class3 23. Suppose a class acts an Actor in the problem domain, how to represent it in the static model? In this scenario you can use “stereotype”. Since stereotype is just a string that gives extra semantic to the particular entity/model element. It is given with in the << >>.
class A
<<>>
attributes

methods.
24. Why does the function arguments are called as “signatures”?
The arguments distinguish functions with the same name (functional polymorphism). The name alone does not necessarily identify a unique function. However, the name and its arguments (signatures) will uniquely identify a function.
In real life we see suppose, in class there are two guys with same name, but they can be easily identified by their signatures. The same concept is applied here.
ex:
class person
{
public:
char getsex();
void setsex(char);
void setsex(int);
};
In the above example we see that there is a function setsex() with same name but with different signature.
21. Differentiate the following notations?
I: :obj1 :obj2
II: :obj1 :obj2
In the above representation I, obj1 sends message to obj2. But in the case of II the data is transferred from obj1 to obj2.
22. USECASE is an implementation independent notation. How will the designer give the implementation details of a particular USECASE to the programmer?
This can be accomplished by specifying the relationship called “refinement” which talks about the two different abstraction of the same thing.
Or example,
calculate pay calculate
class1 class2 class3
23. Suppose a class acts an Actor in the problem domain, how to represent it in the static model?
In this scenario you can use “stereotype”. Since stereotype is just a string that gives extra semantic to the particular entity/model element. It is given with in the << >>.
class A
<<>>
attributes

methods.
24. Why does the function arguments are called as “signatures”?
The arguments distinguish functions with the same name (functional polymorphism). The name alone does not necessarily identify a unique function. However, the name and its arguments (signatures) will uniquely identify a function.
In real life we see suppose, in class there are two guys with same name, but they can be easily identified by their signatures. The same concept is applied here.
ex:
class person
{
public:
char getsex();
void setsex(char);
void setsex(int);
};
In the above example we see that there is a function setsex() with same name but with different signature.

CPP WITH OOAD
1. What do you mean by analysis and design?
Analysis:
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.
Design:
It is the process of adopting/choosing the one among the many, which best accomplishes the users needs. So, simply, it is compromising mechanism.
2. 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.
3. What are the main underlying concepts of object orientation?
Objects, messages, class, inheritance and polymorphism are the main concepts of object orientation.
4. What do u meant by “SBI” of an object?
SBI stands for State, Behavior and Identity. Since every object has the above three.
State:
It is just a value to the attribute of an object at a particular time.
Behaviour:
It describes the actions and their reactions of that object.
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.
5. 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.
6. 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.
Diagram:
client server
(Active) (Passive)
7. What is meant by software development method?
Software development method describes how to model and build software systems in a reliable and reproducible way. To put it simple, methods that are used to represent ones’ thinking using graphical notations.
8. What are models and meta models?
Model:
It is a complete description of something (i.e. system).
Meta model:
It describes the model elements, syntax and semantics of the notation that allows their manipulation.
9. What do you meant by static and dynamic modeling?
Static modeling is used to specify structure of the objects that exist in the problem domain. These are expressed using class, object and USECASE diagrams.
But Dynamic modeling refers representing the object interactions during runtime. It is represented by sequence, activity, collaboration and statechart diagrams.
10. How to represent the interaction between the modeling elements?
Model element is just a notation to represent (Graphically) the entities that exist in the problem domain. e.g. for modeling element is class notation, object notation etc.
Relationships are used to represent the interaction between the modeling elements.
The following are the Relationships.
Association: Its’ just a semantic connection two classes.
e.g.:
Aggregation: Its’ the relationship between two classes which are related in the fashion that master and slave. The master takes full rights than the slave. Since the slave works under the master. It is represented as line with diamond in the master area.
ex:
car contains wheels, etc.

Containment: This relationship is applied when the part contained with in the whole part, dies when the whole part dies.
It is represented as darked diamond at the whole part.
example:
class A{
//some code
};

class B
{
A aa; // an object of class A;
// some code for class B;
};
In the above example we see that an object of class A is instantiated with in the class B. so the object class A dies when the object class B dies.we can represnt it in diagram like this.

Generalization: This relationship used when we want represents a class, which captures the common states of objects of different classes. It is represented as arrow line pointed at the class, which has captured the common states.

Dependency: It is the relationship between dependent and independent classes. Any change in the independent class will affect the states of the dependent class.
DIAGRAM:
class A class B
11. Why generalization is very strong?
Even though Generalization satisfies Structural, Interface, Behaviour properties. It is mathematically very strong, as it is Antisymmetric and Transitive.
Antisymmetric: employee is a person, but not all persons are employees. Mathematically all As’ are B, but all Bs’ not A.
Transitive: A=>B, B=>c then A=>c.
A. Salesman.
B. Employee.
C. Person.
Note: All the other relationships satisfy all the properties like Structural properties, Interface properties, Behaviour properties.
12. Differentiate Aggregation and containment?
Aggregation is the relationship between the whole and a part. We can add/subtract some properties in the part (slave) side. It won’t affect the whole part.
Best example is Car, which contains the wheels and some extra parts. Even though the parts are not there we can call it as car.
But, in the case of containment the whole part is affected when the part within that got affected. The human body is an apt example for this relationship. When the whole body dies the parts (heart etc) are died.
13. Can link and Association applied interchangeably?
No, You cannot apply the link and Association interchangeably. Since link is used represent the relationship between the two objects.
But Association is used represent the relationship between the two classes.
link :: student:Abhilash course:MCA
Association:: student course
14. what is meant by “method-wars”?
Before 1994 there were different methodologies like Rumbaugh, Booch, Jacobson, Meyer etc who followed their own notations to model the systems. The developers were in a dilemma to choose the method which best accomplishes their needs. This particular span was called as “method-wars”
15. Whether unified method and unified modeling language are same or different?
Unified method is convergence of the Rumbaugh and Booch.
Unified modeling lang. is the fusion of Rumbaugh, Booch and Jacobson as well as Betrand Meyer (whose contribution is “sequence diagram”). Its’ the superset of all the methodologies.
16. Who were the three famous amigos and what was their contribution to the object community?
The Three amigos namely,
James Rumbaugh (OMT): A veteran in analysis who came up with an idea about the objects and their Relationships (in particular Associations).
Grady Booch: A veteran in design who came up with an idea about partitioning of systems into subsystems.
Ivar Jacobson (Objectory): The father of USECASES, who described about the user and system interaction.
17. Differentiate the class representation of Booch, Rumbaugh and UML?
If you look at the class representaiton of Rumbaugh and UML, It is some what similar and both are very easy to draw.
Representation: OMT UML.
Diagram:
Booch: In this method classes are represented as “Clouds” which are not very easy to draw as for as the developer’s view is concern.
Diagram:
18. What is an USECASE? Why it is needed?
A Use Case is a description of a set of sequence of actions that a system performs that yields an observable result of value to a particular action.
In SSAD process <=> In OOAD USECASE. It is represented elliptically.
Representation:
19.Who is an Actor?
An Actor is someone or something that must interact with the system.In addition to that an Actor initiates the process(that is USECASE).
It is represented as a stickman like this.
Diagram:

20. What is guard condition?
Guard condition is one, which acts as a firewall. The access from a particular object can be made only when the particular condition is met.
For Example,
customer check customer number ATM.
Here the object on the customer accesses the ATM facility only when the guard condition is met.


30. What is an action class?
Answer:
The simplest and most obvious way to specify an action in C++ is to write a function. However, if the action has to be delayed, has to be transmitted ‘elsewhere’ before being performed, requires its own data, has to be combined with other actions, etc then it often becomes attractive to provide the action in the form of a class that can execute the desired action and provide other services as well. Manipulators used with iostreams is an obvious example.
Explanation:
A common form of action class is a simple class containing just one virtual function.
class Action
{
public:
virtual int do_it( int )=0;
virtual ~Action( );
}
Given this, we can write code say a member that can store actions for later execution without using pointers to functions, without knowing anything about the objects involved, and without even knowing the name of the operation it invokes. For example:
class write_file : public Action
{
File& f;
public:
int do_it(int)
{
return fwrite( ).suceed( );
}
};
class error_message: public Action
{
response_box db(message.cstr( ),"Continue","Cancel","Retry");
switch (db.getresponse( ))
{
case 0: return 0;
case 1: abort();
case 2: current_operation.redo( );return 1;
}
};
A user of the Action class will be completely isolated from any knowledge of derived classes such as write_file and error_message.
31. When can you tell that a memory leak will occur?
Answer:
A memory leak occurs when a program loses the ability to free a block of dynamically allocated memory.
32.What is a parameterized type?
Answer:
A template is a parameterized construct or type containing generic code that can use or manipulate any type. It is called parameterized because an actual type is a parameter of the code body. Polymorphism may be achieved through parameterized types. This type of polymorphism is called parameteric polymorphism. Parameteric polymorphism is the mechanism by which the same code is used on different types passed as parameters.
33. Differentiate between a deep copy and a shallow copy?
Answer:
Deep copy involves using the contents of one object to create another instance of the same class. In a deep copy, the two objects may contain ht same information but the target object will have its own buffers and resources. the destruction of either object will not affect the remaining object. The overloaded assignment operator would create a deep copy of objects.
Shallow copy involves copying the contents of one object into another instance of the same class thus creating a mirror image. Owing to straight copying of references and pointers, the two objects will share the same externally contained contents of the other object to be unpredictable.
Explanation:
Using a copy constructor we simply copy the data values member by member. This method of copying is called shallow copy. If the object is a simple class, comprised of built in types and no pointers this would be acceptable. This function would use the values and the objects and its behavior would not be altered with a shallow copy, only the addresses of pointers that are members are copied and not the value the address is pointing to. The data values of the object would then be inadvertently altered by the function. When the function goes out of scope, the copy of the object with all its data is popped off the stack.
If the object has any pointers a deep copy needs to be executed. With the deep copy of an object, memory is allocated for the object in free store and the elements pointed to are copied. A deep copy is used for objects that are returned from a function.
34. What is an opaque pointer?
Answer:
A pointer is said to be opaque if the definition of the type to which it points to is not included in the current translation unit. A translation unit is the result of merging an implementation file with all its headers and header files.
35. What is a smart pointer?
Answer:
A smart pointer is an object that acts, looks and feels like a normal pointer but offers more functionality. In C++, smart pointers are implemented as template classes that encapsulate a pointer and override standard pointer operators. They have a number of advantages over regular pointers. They are guaranteed to be initialized as either null pointers or pointers to a heap object. Indirection through a null pointer is checked. No delete is ever necessary. Objects are automatically freed when the last pointer to them has gone away. One significant problem with these smart pointers is that unlike regular pointers, they don’t respect inheritance. Smart pointers are unattractive for polymorphic code. Given below is an example for the implementation of smart pointers.
Example:
template
class smart_pointer
{
public:
smart_pointer(); // makes a null pointer
smart_pointer(const X& x) // makes pointer to copy of x

X& operator *( );
const X& operator*( ) const;
X* operator->() const;

smart_pointer(const smart_pointer &);
const smart_pointer & operator =(const smart_pointer&);
~smart_pointer();
private:
//...
};
This class implement a smart pointer to an object of type X. The object itself is located on the heap. Here is how to use it:
smart_pointer

36. What is reflexive association?
Answer:
The ‘is-a’ is called a reflexive association because the reflexive association permits classes to bear the is-a association not only with their super-classes but also with themselves. It differs from a ’specializes-from’ as ’specializes-from’ is usually used to describe the association between a super-class and a sub-class. For example:
Printer is-a printer.
37. What is slicing?
Answer:
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.
Explanation:
Consider the following class declaration:
class base
{
...
base& operator =(const base&);
base (const base&);
}
void fun( )
{
base e=m;
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.
38. What is name mangling?
Answer:
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.
Example:
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
{
public:
int ival;
...
};
ival becomes something like:
// a possible member name mangling
ival__3Bar
Consider this derivation:
class Foo : public Bar
{
public:
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
{
public:
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).
39. What are proxy objects?
Answer:
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
40. Differentiate between declaration and definition in C++.
Answer:
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:
 it declares a function without specifying its body,
 it contains an extern specifier and no initializer or function body,
 it is the declaration of a static class data member without a class definition,
 it is a class name definition,
 it is a typedef declaration.
A definition is a declaration unless:
 it defines a static class data member,
 it defines a non-inline member function.
41. What is cloning?
Answer:
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.
42. Describe the main characteristics of static functions.
Answer:
The main characteristics of static functions include,
 It is without the a this pointer,
 It can’t directly access the non-static members of its class
 It can’t be declared const, volatile or virtual.
 It doesn’t need to be invoked through an object of its class, although for convenience, it may.
43. Will the inline function be compiled as the inline function always? Justify.
Answer:
An inline function is a request and not a command. Hence it won’t be compiled as an inline function always.
Explanation:
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.
44. Define a way other than using the keyword inline to make a function inline.
Answer:
The function must be defined inside the class.
45. How can a ‘::’ operator be used as unary operator?
Answer:
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.
46. What is placement new?
Answer:
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.
frequently asked c pp programs
By admin on April 26th, 2008
146)
main()
{
static int a[3][3]={1,2,3,4,5,6,7,8,9};
int i,j;
static *p[]={a,a+1,a+2};
for(i=0;i<3;i++) j="0;j<3;j++)" x="10,y="8;" x="%d" y="%d" x="10" y="8" i =" 257;" iptr =" &i;" i =" 258;" iptr =" &i;" i="300;" ptr =" &i;" ptr="2;" ptr =" 2" 00101100 =""> 556.
151)
#include
main()
{
char * str = "hello";
char * ptr = str;
char least = 127;
while (*ptr++)
least = (*ptr
printf("%d",least);
}
Answer:
0
Explanation:
After ‘ptr’ reaches the end of the string the value pointed by ‘str’ is ‘\0’. So the value of ‘str’ is less than that of ‘least’. So the value of ‘least’ finally is 0.
152) Declare an array of N pointers to functions returning pointers to functions returning pointers to characters?
Answer:
(char*(*)( )) (*ptr[N])( );
153)
main()
{
struct student
{
char name[30];
struct date dob;
}stud;
struct date
{
int day,month,year;
};
scanf("%s%d%d%d", stud.rollno, &student.dob.day, &student.dob.month, &student.dob.year);
}
Answer:
Compiler Error: Undefined structure date
Explanation:
Inside the struct definition of ‘student’ the member of type struct date is given. The compiler doesn’t have the definition of date structure (forward reference is not allowed in C in this case) so it issues an error.
154)
main()
{
struct date;
struct student
{
char name[30];
struct date dob;
}stud;
struct date
{
int day,month,year;
};
scanf("%s%d%d%d", stud.rollno, &student.dob.day, &student.dob.month, &student.dob.year);
}
Answer:
Compiler Error: Undefined structure date
Explanation:
Only declaration of struct date is available inside the structure definition of ‘student’ but to have a variable of type struct date the definition of the structure is required.
155) There were 10 records stored in “somefile.dat” but the following program printed 11 names. What went wrong?
void main()
{
struct student
{
char name[30], rollno[6];
}stud;
FILE *fp = fopen(“somefile.dat”,”r”);
while(!feof(fp))
{
fread(&stud, sizeof(stud), 1 , fp);
puts(stud.name);
}
}
Explanation:frequently asked C++ Questions
By admin on April 24th, 2008
1. What is a class?
2. What is an object?
3. What is the difference between an object and a class?
4. What is the difference between class and structure?
5. What is public, protected, private?
6. What are virtual functions?
7. What is friend function?
8. What is a scope resolution operator?
9. What do you mean by inheritance?
10. What is abstraction?
11. What is polymorphism? Explain with an example.
12. What is encapsulation?
13. What do you mean by binding of data and functions?
14. What is function overloading and operator overloading?
15. What is virtual class and friend class?
16. What do you mean by inline function?
17. What do you mean by public, private, protected and friendly?
18. When is an object created and what is its lifetime?
19. What do you mean by multiple inheritance and multilevel inheritance? Differentiate between them.
20. Difference between realloc() and free?
21. What is a template?
22. What are the main differences between procedure oriented languages and object oriented languages?
23. What is R T T I ?
24. What are generic functions and generic classes?
25. What is namespace?
26. What is the difference between pass by reference and pass by value?
27. Why do we use virtual functions?
28. What do you mean by pure virtual functions?
29. What are virtual classes?
30. Does c++ support multilevel and multiple inheritance?
31. What are the advantages of inheritance?
32. When is a memory allocated to a class?
33. What is the difference between declaration and definition?
34. What is virtual constructors/destructors?
35. In c++ there is only virtual destructors, no constructors. Why?
36. What is late bound function call and early bound function call? Differentiate.
37. How is exception handling carried out in c++?
38. When will a constructor executed?
39. What is Dynamic Polymorphism?
40. Write a macro for swapping integers

fread reads 10 records and prints the names successfully. It will return EOF only when fread tries to read another record and fails reading EOF (and returning EOF). So it prints the last record again. After this only the condition feof(fp) becomes false, hence comes out of the while loop.
156) Is there any difference between the two declarations,
1. int foo(int *arr[]) and
2. int foo(int *arr[2])
Answer:
No
Explanation:
Functions can only pass pointers and not arrays. The numbers that are allowed inside the [] is just for more readability. So there is no difference between the two declarations.
157) What is the subtle error in the following code segment?
void fun(int n, int arr[])
{
int *p=0;
int i=0;
while(i++
p = &arr[i];
*p = 0;
}
Answer & Explanation:
If the body of the loop never executes p is assigned no address. So p remains NULL where *p =0 may result in problem (may rise to runtime error “NULL pointer assignment” and terminate the program).
158) What is wrong with the following code?
int *foo()
{
int *s = malloc(sizeof(int)100);
assert(s != NULL);
return s;
}
Answer & Explanation:
assert macro should be used for debugging and finding out bugs. The check s != NULL is for error/exception handling and for that assert shouldn’t be used. A plain if and the corresponding remedy statement has to be given.
159) What is the hidden bug with the following statement?
assert(val++ != 0);
Answer & Explanation:
Assert macro is used for debugging and removed in release version. In assert, the experssion involves side-effects. So the behavior of the code becomes different in case of debug version and the release version thus leading to a subtle bug.
Rule to Remember:
Don’t use expressions that have side-effects in assert statements.
160)
void main()
{
int *i = 0x400; // i points to the address 400
*i = 0; // set the value of memory location pointed by i;
}
Answer:
Undefined behavior
Explanation:
The second statement results in undefined behavior because it points to some location whose value may not be available for modification. This type of pointer in which the non-availability of the implementation of the referenced location is known as ‘incomplete type’.
161)
#define assert(cond) if(!(cond)) \
(fprintf(stderr, "assertion failed: %s, file %s, line %d \n",#cond,\
__FILE__,__LINE__), abort())

void main()
{
int i = 10;
if(i==0)
assert(i < 100);
else
printf("This statement becomes else for if in assert macro");
}
Answer:
No output
Explanation:
The else part in which the printf is there becomes the else for if in the assert macro. Hence nothing is printed.
The solution is to use conditional operator instead of if statement,
#define assert(cond) ((cond)?(0): (fprintf (stderr, “assertion failed: \ %s, file %s, line %d \n”,#cond, __FILE__,__LINE__), abort()))
Note:
However this problem of “matching with nearest else” cannot be solved by the usual method of placing the if statement inside a block like this,
#define assert(cond) { \
if(!(cond)) \
(fprintf(stderr, “assertion failed: %s, file %s, line %d \n”,#cond,\
__FILE__,__LINE__), abort()) \
}
162) Is the following code legal?
struct a
{
int x;
struct a b;
}
Answer:
No
Explanation:
Is it not legal for a structure to contain a member that is of the same
type as in this case. Because this will cause the structure declaration to be recursive without end.
163) Is the following code legal?
struct a
{
int x;
struct a *b;
}
Answer:
Yes.
Explanation:
*b is a pointer to type struct a and so is legal. The compiler knows, the size of the pointer to a structure even before the size of the structure
is determined(as you know the pointer to any type is of same size). This type of structures is known as ‘self-referencing’ structure.
164) Is the following code legal?
typedef struct a
{
int x;
aType *b;
}aType
Answer:
No
Explanation:
The typename aType is not known at the point of declaring the structure (forward references are not made for typedefs).
165) Is the following code legal?
typedef struct a aType;
struct a
{
int x;
aType *b;
};
Answer:
Yes
Explanation:
The typename aType is known at the point of declaring the structure, because it is already typedefined.
166) Is the following code legal?
void main()
{
typedef struct a aType;
aType someVariable;
struct a
{
int x;
aType *b;
};
}
Answer:
No
Explanation:
When the declaration,
typedef struct a aType;
is encountered body of struct a is not known. This is known as ‘incomplete types’.
167)
void main()
{
printf(“sizeof (void *) = %d \n“, sizeof( void *));
printf(“sizeof (int *) = %d \n”, sizeof(int *));
printf(“sizeof (double *) = %d \n”, sizeof(double *));
printf(“sizeof(struct unknown *) = %d \n”, sizeof(struct unknown *));
}
Answer :
sizeof (void *) = 2
sizeof (int *) = 2
sizeof (double *) = 2
sizeof(struct unknown *) = 2
Explanation:
The pointer to any type is of same size.
168)
char inputString[100] = {0};
To get string input from the keyboard which one of the following is better?
1) gets(inputString)
2) fgets(inputString, sizeof(inputString), fp)
Answer & Explanation:
The second one is better because gets(inputString) doesn’t know the size of the string passed and so, if a very big input (here, more than 100 chars) the charactes will be written past the input string. When fgets is used with stdin performs the same operation as gets but is safe.
169) Which version do you prefer of the following two,
1) printf(“%s”,str); // or the more curt one
2) printf(str);
Answer & Explanation:
Prefer the first one. If the str contains any format characters like %d then it will result in a subtle bug.
170)
void main()
{
int i=10, j=2;
int *ip= &i, *jp = &j;
int k = *ip/*jp;
printf(“%d”,k);
}
Answer:
Compiler Error: “Unexpected end of file in comment started in line 5”.
Explanation:
The programmer intended to divide two integers, but by the “maximum munch” rule, the compiler treats the operator sequence / and * as /* which happens to be the starting of comment. To force what is intended by the programmer,
int k = *ip/ *jp;
// give space explicity separating / and *
//or
int k = *ip/(*jp);
// put braces to force the intention
will solve the problem.
171)
void main()
{
char ch;
for(ch=0;ch<=127;ch++)
printf(“%c %d \n“, ch, ch);
}
Answer:
Implementaion dependent
Explanation:
The char type may be signed or unsigned by default. If it is signed then ch++ is executed after ch reaches 127 and rotates back to -128. Thus ch is always smaller than 127.
172) Is this code legal?
int *ptr;
ptr = (int *) 0x400;
Answer:
Yes
Explanation:
The pointer ptr will point at the integer in the memory location 0×400.
173)
main()
{
char a[4]="HELLO";
printf("%s",a);
}
Answer:
Compiler error: Too many initializers
Explanation:
The array a is of size 4 but the string constant requires 6 bytes to get stored.
174)
main()
{
char a[4]="HELL";
printf("%s",a);
}
Answer:
HELL%@!~@!@???@~~!
Explanation:
The character array has the memory just enough to hold the string “HELL” and doesnt have enough space to store the terminating null character. So it prints the HELL correctly and continues to print garbage values till it accidentally comes across a NULL character.
175)
main()
{
int a=10,*j;
void *k;
j=k=&a;
j++;
k++;
printf("\n %u %u ",j,k);
}
Answer:
Compiler error: Cannot increment a void pointer
Explanation:
Void pointers are generic pointers and they can be used only when the type is not known and as an intermediate address storage type. No pointer arithmetic can be done on it and you cannot apply indirection operator (*) on void pointers.
176)
main()
{
extern int i;
{ int i=20;
{
const volatile unsigned i=30; printf("%d",i);
}
printf("%d",i);
}
printf("%d",i);
}
int i;
177) Printf can be implemented by using __________ list.
Answer:
Variable length argument lists
178)
char *someFun()
{
char *temp = "string constant";
return temp;
}
int main()
{
puts(someFun());
}
Answer:
string constant
Explanation:
The program suffers no problem and gives the output correctly because the character constants are stored in code/data area and not allocated in stack, so this doesn’t lead to dangling pointers.
179)
char *someFun1()
{
char temp[ ] = "string";
return temp;
}
char *someFun2()
{
char temp[ ] = {‘s’, ‘t’,’r’,’i’,’n’,’g’};
return temp;
}
int main()
{
puts(someFun1());
puts(someFun2());
}
Answer:
Garbage values.
Explanation:
Both the functions suffer from the problem of dangling pointers. In someFun1() temp is a character array and so the space for it is allocated in heap and is initialized with character string “string”. This is created dynamically as the function is called, so is also deleted dynamically on exiting the function so the string data is not available in the calling function main() leading to print some garbage values. The function someFun2() also suffers from the same problem but the problem can be easily identified in this case.


frequently asked C++ Questions
By admin on April 24th, 2008
1. What is a class?
2. What is an object?
3. What is the difference between an object and a class?
4. What is the difference between class and structure?
5. What is public, protected, private?
6. What are virtual functions?
7. What is friend function?
8. What is a scope resolution operator?
9. What do you mean by inheritance?
10. What is abstraction?
11. What is polymorphism? Explain with an example.
12. What is encapsulation?
13. What do you mean by binding of data and functions?
14. What is function overloading and operator overloading?
15. What is virtual class and friend class?
16. What do you mean by inline function?
17. What do you mean by public, private, protected and friendly?
18. When is an object created and what is its lifetime?
19. What do you mean by multiple inheritance and multilevel inheritance? Differentiate between them.
20. Difference between realloc() and free?
21. What is a template?
22. What are the main differences between procedure oriented languages and object oriented languages?
23. What is R T T I ?
24. What are generic functions and generic classes?
25. What is namespace?
26. What is the difference between pass by reference and pass by value?
27. Why do we use virtual functions?
28. What do you mean by pure virtual functions?
29. What are virtual classes?
30. Does c++ support multilevel and multiple inheritance?
31. What are the advantages of inheritance?
32. When is a memory allocated to a class?
33. What is the difference between declaration and definition?
34. What is virtual constructors/destructors?
35. In c++ there is only virtual destructors, no constructors. Why?
36. What is late bound function call and early bound function call? Differentiate.
37. How is exception handling carried out in c++?
38. When will a constructor executed?
39. What is Dynamic Polymorphism?
40. Write a macro for swapping integers