C++ Interview Questions and Answers for Freshers
- What is difference between C and C++ ?
C++ is Multi-Paradigm ( not pure OOP, supports both procedural and object oriented) while C follows procedural style programming.
In C data security is less, but in C++ you can use modifiers for your class members to make it inaccessible from outside.
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 ).
C++ supports function overloading while C does not support it.
C++ allows use of functions in structures, but C does not permit that.
C++ supports reference variables ( two variables can point to same memory location ). C does not support this.
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. - What is a class?
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. - 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 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 classIn the class Person, access to the data field age is protected by declaring it as private and providing public access methods. 6. 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.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.7. 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,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. 8. In how many ways we can initialize an int variable in C++?In c++, variables can be initialized in two ways, the traditional C++ initialization using “=” operator and second using the constructor notation.Traditional C++ initilizationvariable i will get initialized to 10. Using C++ constructor notationWhat is implicit conversion/coercion in c++?Implicit conversions are performed when a type (say T) is used in a context where a compatible type (Say F) is expected so that the type T will be promoted to type F.short a = 2000 + 20;In the above example, variable a will get automatically promoted from short to int. This is called implicit conversion/coercion in c++. 9. What are C++ inline functions? C++ inline functions are special functions, for which the compiler replaces the function call with body/definition of function. Inline functions makes the program execute faster than the normal functions, since the overhead involved in saving current state to stack on the function call is avoided. By giving developer the control of making a function as inline, he can further optimize the code based on application logic. But actually, it’s the compiler that decides whether to make a function inline or not regardless of it’s declaration. Compiler may choose to make a non inline function inline and vice versa. Declaring a function as inline is in effect a request to the compiler to make it inline, which compiler may ignore. So, please note this point for the interview that, it is upto the compiler to make a function inline or not. 10. What do you mean by translation unit in c++?We organize our C++ programs into different source files (.cpp, .cxx etc). When you consider a source file, at the preprocessing stage, some extra content may get added to the source code ( for example, the contents of header files included) and some content may get removed ( for example, the part of the code in the #ifdef of #ifndef block which resolve to false/0 based on the symbols defined). This effective content is called a translation unit. In other words, a translation unit consists ofContents of source filePlus contents of files included directly or indirectly Minus source code lines ignored by any conditional pre processing directives ( the lines ignored by #ifdef,#ifndef etc)