Few
Facts for your reference in C++:: Make sure you go through it ....
1. What is difference between C and C++?
[This is a usual C or C++ interview question, mostly the first one you will face if you are fresher or appearing for campus interview. When answering this question please make sure you don't give the text book type explanations, instead give examples from real software scenario. Answer for this interview question can include below points, though it’s not complete list. This question itself can be a 1day interview !!!]
1. C++ is Multi-Paradigm (not pure OOP, supports both procedural and object oriented) while C follows procedural style programming.
2. In C data security is less, but in C++ you can use modifiers for your class members to make it inaccessible from outside.
3. C follows top-down approach (solution is created in step by step manner, like each step is processed into details as we proceed) but C++ follows a bottom-up approach ( where base elements are established first and are linked to make complex solutions ).
4. C++ supports function overloading while C does not support it.
5. C++ allows use of functions in structures, but C does not permit that.
6. C++ supports reference variables ( two variables can point to same memory location ). C does not support this.
7. C does not have a built in exception handling framework, though we can emulate it with other mechanism. C++ directly supports exception handling, which makes life of developer easy.
2. What is a class?
[Probably this would be the first question for a Java/C++ technical interview for fresher's and sometimes for experienced as well. Try to give examples when you answer this question.]
Class defines a datatype, it's type definition of category of thing(s). But a class actually does not define the data, it just specifies the structure of data. To use them you need to create objects out of the class. Class can be considered as a blueprint of a building, you can not stay inside blueprint of building, you need to construct building(s) out of that plan. You can create any number of buildings from the blueprint, similarly you can create any number of objects from a class.
1. class Vehicle
2. {
3. public:
4. int numberOfTyres;
5. double engineCapacity;
6. void drive(){
7. // code to drive the car
8. }
9. };
3. What is an Object/Instance?
Object is the instance of a class, which is concrete. From the above example, we can create instance of class Vehicle as given below
1. Vehicle vehicleObject;
We can have different objects of the class Vehicle, for example we can have Vehicle objects with 2 tyres, 4tyres etc. Similarly different engine capacities as well.
4. What do you mean by C++ access specifiers ?
[Questions regarding access specifiers are common not just in c++ interview but for other object oriented language interviews as well.]
Access specifiers are used to define how the members (functions and variables) can be accessed outside the class. There are three access specifiers defined which are public, private, and protected
• private:
Members declared as private are accessible only with in the same class and they cannot be accessed outside the class they are declared.
• public:
Members declared as public are accessible from any where.
• protected:
Members declared as protected can not be accessed from outside the class except a child class. This access specifier has significance in the context of inheritance.
5. What are the basics concepts of OOP?
[ A must OOP / c++ interview question for freshers (some times asked in interviews for 1-2 years experienced also), which everybody answers as well. But the point is, it's not about the answer, but how you apply these OOPs concepts in real life. You should be able to give real life examples for each of these concepts, so prepare yourself with few examples before appearing for the interview. It has seen that even the experienced people get confused when it comes to the difference between basic OOP concepts, especially abstraction and encapsulation.]
• Classes and Objects
Refer Questions 2 and 3 for the concepts about classes and objects
• Encapsulation
Encapsulation is the mechanism by which data and associated operations/methods are bound together and thus hide the data from outside world. It's also called data hiding. In c++, encapsulation achieved using the access specifiers (private, public and protected). Data members will be declared as private (thus protecting from direct access from outside) and public methods will be provided to access these data. Consider the below class
1. class Person
2. {
3. private:
4. int age;
5. public:
6. int getAge(){
7. return age;
8. }
9. int setAge(int value){
10. if(value > 0){
11. age = value;
12. }
13. }
14. };
In the class Person, access to the data field age is protected by declaring it as private and providing public access methods. What would have happened if there was no access methods and the field age was public? Anybody who has a Person object can set an invalid value (negative or very large value) for the age field. So by encapsulation we can preventing direct access from outside, and thus have complete control, protection and integrity of the data.
• Data abstraction
Data abstraction refers to hiding the internal implementations and show only the necessary details to the outside world. In C++ data abstraction is implemented using interfaces and abstract classes.
1. class Stack
2. {
3. public:
4. virtual void push(int)=0;
5. virtual int pop()=0;
6. };
7.
8. class MyStack : public Stack
9. {
10. private:
11. int arrayToHoldData[]; //Holds the data from stack
12.
13. public:
14. void push(int) {
15. // implement push operation using array
16. }
17. int pop(){
18. // implement pop operation using array
19. }
20. };
In the above example, the outside world only need to know about the Stack class and its push, pop operations. Internally stack can be implemented using arrays or linked lists or queues or anything that you can think of. This means, as long as the push and pop method performs the operations work as expected, you have the freedom to change the internal implementation with out affecting other applications that use your Stack class.
• Inheritance
Inheritance allows one class to inherit properties of another class. In other words, inheritance allows one class to be defined in terms of another class.
1. class SymmetricShape
2. {
3. public:
4. int getSize()
5. {
6. return size;
7. }
8. void setSize(int w)
9. {
10. size = w;
11. }
12. protected:
13. int size;
14. };
15.
16. // Derived class
17. class Square: public SymmetricShape
18. {
19. public:
20. int getArea()
21. {
22. return (size * size);
23. }
24. };
In the above example, class Square inherits the properties and methods of class SymmetricShape. Inheritance is the one of the very important concepts in C++/OOP. It helps to modularize the code, improve reusability and reduces tight coupling between components of the system.
6. What is the use of volatile keyword in c++? Give an example.
Most of the times compilers will do optimization to the code to speed up the program. For example in the below code,
1. int a = 10;
2. while( a == 10){
3. // Do something
4. }
compiler may think that value of 'a' is not getting changed from the program and replace it with 'while(true)', which will result in an infinite loop. In actual scenario the value of 'a' may be getting updated from outside of the program.
Volatile keyword is used to tell compiler that the variable declared using volatile may be used from outside the current scope so that compiler wont apply any optimization. This matters only in case of multi-threaded applications.
In the above example if variable 'a' was declared using volatile, compiler will not optimize it. In shot, value of the volatile variables will be read from the memory location directly.
What is the full form of OOPS?
Object Oriented Programming System.
What is a class?
Class is a blue print which reflects the entities attributes and actions. Technically defining a class is designing an user defined data type.
What is an object?
An instance of the class is called as object.
List the types of inheritance supported in C++.What is the role of protected access specifier?
Single, Multiple, Multilevel, Hybrid and Hierarchical inheritance.
If a class member is protected then it is accessible in the inherited class. However, outside the both the private and protected members are not accessible.
What is encapsulation?
The process of binding the data and the functions acting on the data together in an entity (class) called as encapsulation.
What is abstraction?
Abstraction refers to hiding the internal implementation and exhibiting only the necessary details.
What is inheritance?
Inheritance is the process of acquiring the properties of the existing class into the new class. The existing class is called as base/parent class and the inherited class is called as derived/child class.
Explain the purpose of the keyword volatile?
Declaring a variable volatile directs the compiler that the variable can be changed externally. Hence avoiding compiler optimization on the variable reference.
What is an inline function?
A function prefixed with the keyword inline before the function definition is called as inline function. The inline functions are faster in execution when compared to normal functions as the compiler treats inline functions as macros.
What is a storage class?
Storage class specifies the life or scope of symbols such as variable or functions. Mention the storage classes names in C++. The following are storage classes supported in C++ auto, static, extern, register and mutable.
What is the role of mutable storage class specifier?
A constant class object’s member variable can be altered by declaring it using mutable storage class specifier. Applicable only for non-static and non-constant member variable of the class. Distinguish between shallow copy and deep copy. Shallow copy does memory dumping bit-by-bit from one object to another. Deep copy is copy field by field from object to another. Deep copy is achieved using copy constructor or overloading assignment operator.
What is a pure virtual function?
A virtual function with no function body and assigned with a value zero is called as pure virtual function.
What is an abstract class in C++?
A class with at least one pure virtual function is called as abstract class. We cannot instantiate an abstract class.
What is a reference variable in C++?
A reference variable is an alias name for the existing variable. Which mean both the variable name and reference variable point to the same memory location. Therefore, updating on the original variable can be achieved using reference variable too.
What is role of static keyword on class member variable?
A static variable does exit though the objects for the respective class are not created. Static member variable share a common memory across all the objects created for the respective class. A static member variable can be referred using the class name itself.
Explain the static member function?
A static member function can be invoked using the class name as it exits before class objects comes into existence. It can access only static members of the class. Name the data type which can be used to store wide characters in C++.
wchar_t
What are/is the operator/operators used to access the class members?
Dot (.) and Arrow ( -> )
Can we initialize a class/structure member variable as soon as the same is defined?
No, Defining a class/structure is just a type definition and will not allocated memory for the same.
What is the data type to store the Boolean value?
bool, is the new primitive data type introduced in C++ language.
What is function overloading?
Defining several functions with the same name with unique list of parameters is called as function overloading.
What is operator overloading?
Defining a new job for the existing operator w.r.t the class objects is called as operator overloading.
Do we have a String primitive data type in C++?
No, it’s a class from STL (Standard template library).
Name the default standard streams in C++.
cin, cout, cerr and clog.
Which access specifiers can help to achieve data hiding in C++?
Private & Protected.
When a class member is defined outside the class, which operator can be used to associate the function definition to a particular class?
Scope resolution operator (::)
What is a destructor? Can it be overloaded?
A destructor is the member function of the class which is having the same name as the class name and prefixed with tilde (~) symbol. It gets executed automatically w.r.t the object as soon as the object loses its scope. It cannot be overloaded and the only form is without the parameters.
What is a constructor?
A constructor is the member function of the class which is having the same as the class name and gets executed automatically as soon as the object for the respective class is created.
What is a default constructor? Can we provide one for our class?
Every class does have a constructor provided by the compiler if the programmer doesn’t provides default constructor. A programmer provided constructor with no parameters is called as default constructor. In such case compiler doesn’t provides the constructor.
Which operator can be used in C++ to allocate dynamic memory?
‘new’ is the operator can be used for the same.
What is the purpose of ‘delete’ operator?
‘delete’ operator is used to release the dynamic memory which was created using ‘new’ operator.
Can I use malloc() function of C language to allocate dynamic memory in C++?
Yes, as C is the subset of C++, we can all the functions of C in C++ too.
Can I use ‘delete’ operator to release the memory which was allocated using malloc() function of C language?
No, we need to use free() of C language for the same.
What is a friend function?
A function which is not a member of the class but still can access all the member of the class is called friend. To make it happen we need to declare within the required class following the keyword ‘friend’.
What is a copy constructor?
A copy constructor is the constructor which take same class object reference as the parameter. It gets automatically invoked as soon as the object is initialized with another object of the same class at the time of its creation.
Does C++ supports exception handling? If so what are the keywords involved in achieving the same.
C++ does supports exception handling. try, catch & throw are keyword used for the same.
Explain the pointer – this.
This, is the pointer variable of the compiler which always holds the current active object’s address.
What is the difference between the keywords struct and class in C++?
By default the members of struct are public and by default the members of the class are private.
Can we implement all the concepts of OOPS using the keyword struct?
Yes.
What is the block scope variable in C++?
A variable whose scope is applicable only within a block is said so. Also a variable in C++ can be declared anywhere within the block.
What is the role of the file opening mode ios::trunk?
If the file already exists, its content will be truncated before opening the file.
