Question : Why main function is special in C++ ?

Answer : Whenever a C++ program is executed, execution of the program starts and ends at main(). The main is the driver function of the program. If it is not present in a program, no execution can take place.

Question : What is run-time error, logical error and syntax error?

Answer : Syntax error - The errors which are traced by the compiler during compilation, due to wrong grammar for the language used in the program, are called syntax errors.
For example, cin<<a; // instead of extraction operator insertion operator is used.
Run time Error - The errors encountered during execution of the program, due to unexpected input or output are called run-time error.
For example - a=n/0; // division by zero
Logical Error - These errors are encountered when the program does not give the desired output, due to wrong logic of the program.
For example : remainder = a+b // instead of using % operator + operator is used.

Question : What is the role of #include directive in C++?

Answer : The preprocessor directive #include tells the complier to insert another file into your source file. In effect, #include directive is replaced by the contents of the file indicated.

Question : What is compiler and linker?

Answer : Compiler - It is a program which converts the program written in a programming language to a program in machine language.
Linker - It is a program which links a complied program to the necessary library routines, to make it an executable program. more details

Question : Why is char often treated as integer data type in C++ ?

Answer : The memory implementation of char data type is in terms of the number code. Therefore, it is said to be another integer data type.

Question : What is type conversion in C++ ?

Answer : When two operands of different data types are encountered in the same expression, the variable of lower data type is automatically converted to the data tpes of variable with higher data type, and then the expression is calculated.
For example: int a=98; float b=5; cout<<a/3.0; //converts to float type, since 3.0 is of float type.
cout<<a/b; // converts a temporarily to float type, since b is of float type, and gives the result 19.6.

Question : What is type casting in C++ ?

Answer : Type casting refers to the data type conversions specified by the programmer, as opposed to the automatic type conversions. This can be done when the compiler does not do the conversions automatically. Type casting can be done to higher or lower data type.
For example : cout<<(float)12/5; //displays 2.4, since 12 is converted to float type.

Question : What is the effect of absence of break in switch case in C++ ?

Answer : The break keyword causes the entire switch statement to exit, and the control is passed to statement following the switch.. case construct. Without break, the control passes to the statements for the next case. The break statement is optional in switch..case construct.

Question : In control structure switch-case what is the purpose of default in C++ ?

Answer : This keyword gives the switch..case construct a way to take an action if the value of the switch variable does not match with any of the case constants. No break statement is necessary after default case, since the control is already at the end of switch..case construct. The default is optional in case of switch..case construct.

Question : What is the difference between while and do-while loop?

Answer : While is an Entry Controlled Loop, the body of the loop may not execute even once if the test expression evaluates to be false the first time, whereas in do..while, the loop is executed at least once whether the condition holds true the first time or not. more details

Question : What is the difference between call by value and call by reference in a user defined function in C++?

Answer : The value of the actual parameters in the calling function do not get affected when the arguments are passed using call by value method, since actual and formal parameters have different memory locations.
The values of the formal parameters affect the values of actual parameters in the calling function, when the arguments are passed using call by reference method. This happens since the formal parameters are not allocated any memory, but they refer to the memory locations of their corresponding actual parameters. more details

Question : What is preprocessor directive?

Answer : A preprocessor directive is an instruction to the complier itself. A part of compiler called preprocessor deals with these directives, before real compilation process. # is used as preprocessor directive in C++.

Question : What is the difference between local variable and global variable?

Answer : Local variables are those variables which are declared within a function or a compound statement and these variables can only be used within that function/scope. They cannot be accessed from outside the function or a scope of it's declaration. This means that we can have variables with the same names in different functions/scope. Local variables are local to the function/scope in which they are declared.
Global variables are those variables which are declared in the beginning of the program. They are not declared within a function. So, these variables can be accessed by any function of the program. So, global variables are global to all the functions of the program.

Question : What is the role of #define in C++?

Answer : It is a preprocessor directive to define a macro in a C++ program. Macros provide a mechanism for token replacement with or without a set of formal, function line parameters. For example :
#define PIE 3.1416
#define AVG(A,B,C) (A+B+C)/3

Question : What are the major differences between Object Oriented Programming and Procedural Programming?

Object Oriented Programming
*Emphasis on data
*Follow bottom up approach in program design
*Concept of Data hiding prevents accidental change in the data
*Polymorphism, inheritance, Data Encapsulation possible
Procedural Programming
*Emphasis on doing things (function)
*Follow top-down approach in program design
*Due to presence of global variables, there are possibilities of accidental change in data. more details

Question : What are the basic concepts of OOP?

Answer :Data Abstraction, Data Hiding, Data Encapsulation, Inheritance and Polymorphism are the basic concepts of OOP. more details

Question : How is OOP implement in C++?

Answer : A class binds together data and its associated function under one unit thereby enforcing encapsulation.
The private and protected member remain hidden from outside world. Thus a class enforces data hiding
The outside world is given only the essential information through public members, thereby enforcing abstraction.

Question : What is abstract class?

Answer : A class with no instances (no objects) is known as abstract class.

Question : What is concrete class?

Answer : A class having objects is known as concrete class.

Question : What is a constructor? What are its features?

Answer : It is a member function of class with the following unique features.
It has same name as the name of the class they belong to.
It has no return type.
It is defined in public visibility mode.
It is automatically called & executed when an object is declared/created.
Constructor can be overloaded. more details

Question : What does a destructor do?

Answer : A destructor deinitializes an object and deallocates all allocated resources.

Question : Define inheritance.

Answer : Inheritance is a process of creating new classes (derived classes) from existing classes (base classes). The derived classes not only inherit capabilities of the base class but also can add new features of own. The most important aspect of inheritance is that it allows reusability of code. more details

Question : Define Base class and derived class.

Answer : Base Class: A class from which another class inherits.
Derived Class: A class inheriting properties from another class.

Question : What are the different forms of inheritance in C++ ?

Answer : Single level inheritance, Multilevel inheritance, Hierarchical inheritance, Multiple inheritance and Hybrid inheritance. more details

Question : What is virtual base class in C++ ? What is its significance?

Answer : Multipath inheritance may lead to duplication of inherited members from a grandparent base class. This may be avoided by making the common base class a virtual base class. When a class is made a virtual base class, C++ takes necessary care to see that only one copy of that class is inherited. more details

Question : How are binary files different from text files in C++?

Answer : A text file store information in ASCII characters. In text files, each line of text is terminated, with a special character known as EOL character.
A binary file store information in the same format in which the information is held in memory. In binary file, there is no delimeter for a line.

Question : What is a stream? Name the streams generally used for file I/O.

Answer : A stream is a sequence of byte.
ofstream: Stream class to write on files
ifstream: Stream class to read from files
fstream: Stream class to both read and write from/to files. more details

Question : Difference between get() and getline().

Answer : get() does not extract the delimeter newline character from input stream. On the other hand getline() does extract the delimeter newline character from the input stream so that the stream is empty after getline() is over.

Question : Difference between ios::app and ios::out.

Answer : The ios::out is the default mode of ofstream. With the mode of the file does not exist, it gets created but if the file exists then its existing contents get deleted.
The ios::app is output mode of ofstream. With the mode of the file does not exist, it gets created but if the file exists then its existing contents are retained and new information is appended to it. more details

Question : What is pointer?

Answer : Pointer is an address of a memory location. A variable, which holds an address of a memory location, is known as a Pointer variable (or Simply Pointer). For example int *P; more details

Question : What is pointer arithmetic ? How is it performed?

Answer : Some arithmetic operators can be used with pointers:
Increment and decrement operators ++, --
Integers can be added to or subtracted from pointers using the operators +, -, +=, and -=
Each time a pointer is incremented by 1, it points to the memory location of the next element of its base type.
If "p" is a character pointer then "p++" will increment "p" by 1 byte.
If "p" were an integer pointer its value on "p++" would be incremented by 2 bytes.

Question : Differentiate between static and dynamic allocation of memory.

Answer : In the static memory allocation, the amount of memory to be allocated is predicted and preknown. This memory is allocated during the compilation itself.
In the dynamic memory allocation, the amount of memory allocated is not known beforehead. This memory is allocated during run time as and when required.

Question : What do you understand by memory leaks? How can memory leaks be avoided?

Answer : Memory leak is a situation in which there lie so many orphaned memory blocks that are still allocated but no pointers are referencing to them.

Question : What is this pointer? What is its Significance?

Answer : The this pointer is an object pointer which points to the currently calling object, The this pointer is, by default, available to each called member function.

Question : What is the full form of LIFO? Give an example of LIFO list?

Answer : Full form of LIFO is LAST IN FIRST OUT. An example of LIFO list is stack. Stack is a linear data structure in which insertion and deletion of elements takes place only one end known as TOP.

Question : What is the full form of FIFO? What is FIFO list technically called?

Answer : Full form of FIFO is FIRST IN FIRST OUT. An example of FIFO list is Queue. Queue is a linear data structure in which insertion and deletion of elements takes place from two opposite ends rear and front respectively.

Question : What are the preconditions for Binary search to be performed on a single dimensional array?

Answer : Precondition for Binary search to be performed on a single dimensional array is array should be sorted. more details