SOME GENERAL QUESTIONS ABOUT C++

Questions and Answers C++ 

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.

 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.

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