Viva Questions

CHAPTER1 REVIEW OF C++

1.        What are tokens, identifiers, literals. Pl learn the naming conventions of these.

·         Tokens- Smallest individual unit. Following are the tokens

·         Keyword-Reserve word having special meaning the language and can’t be used as

identifier.

·         Identifiers-Names given to any variable, function, class, union etc. Naming convention (rule) for writing identifier is as under:

o    First letter of identifier is always alphabet.

o    Reserve word cannot be taken as identifier name.

o    No special character in the name of identifier except under score sign ‘_’.

·         Literals-Value of specific data type assign to a variable or constant. Four type of Literals: i) Integer Literal   i.e int x =10

 ii) Floating point Literal  i.e float x=123.45

iii)Character Literal  i.e char x= ‘a’, enclosed in single quotes and single character only.

iv) String Literal  i.e cout<< “Welcome” , anything enclosed in double quotes

·         Operator – performs some action on data 

·         Arithmetic(+,-,*,/,%) 

·         Assignment  operator (=)

·         Increment / Decrement  (++, --)

·         Relational/comparison (<,>,<=,>=,==,!=).

·         Logical(AND(&&),OR(||),NOT(!).

·         Conditional (? :)

2.        Name simple, compound and user defined data types.

·         Fundamental type/simple : Which are not composed any other data type i.e. int, char, float and void

·         Derived data type /compound: Which are made up of fundamental data type i.e array, function, class etc

·         User defined: they are tailor made data types created by the user eg structures and classes

3.        What are macros? How they are implemented in C++?

Macros: These are very simple inline functions which are written before main().These are on line functions returning very simple calculations eg area of square circle etc.When the compiler encounter a function call the function call is replaced by the program code. This ensures faster processing by removing the overhead required for transferring control to function definition.

eg

#include <iostream.h>

#define area_square(s) s*s

void main()

{ cout<<"Area of square: "<<area_square(4);

}

output:

Area of square: 16

4.        What is typedef? How to define another name for string, int, float or char datatypes?

Used to define new data type name.

e.g. typedef char Str80[80];  

Str80   str;

So the new name for char data type here will be Str80. str is a variable of Str80 having size as 80 char.

eg 2. typedef int age;

age x;

Here Age is the new name for int data type . x is a variable having age data type.

5.        How can you call a variable by two names?

By using alias name as in reference variables. Eg When we pass a variable by reference in a function, the same variable has two names, one in the calling function and the other in the function definition.

Eg

void func1( int & marks)

{ if(marks>90)                                        alias name

                cout<<”V.Good”;

   else

                Cout<<”Good”;

}

void main()

{              int m;

cout<<”Enter marks”;

                cin>> m;

                func1(m);

}                                                  actual name

6.        What are reference variables?

A reference is an alternative name for an object or variable. A reference variable provides an alias for a previously defined variable. A reference declaration consists of base type , an & (ampersand), a reference variable name equated to a variable name .the general syntax form of declaring a reference variable is as follows.

Type & ref_variable = variable_name;

Where  type is any valid C++ datatype, ref_variable is the name of reference variable that will point to variable denoted by variable_name.

e.g int a= 10;

 int &b= a;

then the value of a is 10 and the value of b is also 10;

7.        Diff between ‘’h’’ & ‘h’

Here “h” is a string having size 2 bytes. ‘h’ is a character constant with size 1 byute.

8.        Diff between getch ( ) & getche( )

getch() and getche() both accept a single character from inout stream, getche also shows the character on the screen( e stands for echo).

9.        Diff between toupper( ) & isupper( )

toupper()-converts given character to uppercase

isupper()- returns true if the character is uppercase else returns false.

10.     Diff between if (i=2) & if(i= =2)

(i=2) : this assigns value 2 to i

 if(i= =2): this checks whether the value of I is 2 or not and returns true or false accordingly.

11.     use of # include

#include is the preprocessor directive used in C++ programs. This statement tells the

compiler to include the specified file into the program. This line is compiled by the processor

before the compilation of the program.

 e.g #include<iostream.h>

the above line include the header file iostream into the program for the smooth running of the

program.

12.     What is typecasting?

Type Casting

Explicit type casting operator

Type casting operators allow you to convert the data type of a given variable  to another. There are several ways to do this

1.To precede the expression to be converted by the  new type enclosed between parentheses ( ) :

int i;

float f =3.14;

i = ( int ) f;

The previous code converts the float number 3.14 to an integer value (3), the remainder is lost. Here, the typecasting operator was (int).

2. Another way to do the same thing in C++ is using the functional notation: preceding the expression to be converted by the type and enclosing the expression between parentheses:

 i = int (f );

Both ways of type casting are valid in C++.

Implicit conversions are automatically performed when a value is copied to a compatible type. For example:

Char ch=’A’;

Int b=ch;

Here, the value of ch is promoted from char to int without the need of any explicit operator.

13.     Compilation and Linking

Compilation refers to the processing of source code files (.c, .cc, or .cpp) and the creation of

an 'object' file. This step doesn't create anything the user can actually run. Instead, the

compiler merely produces the machine language instructions that correspond to the source

code file that was compiled. For instance, if you compile (but don't link) three separate files,

you will have three object files created as output, each with the name <filename>.o or

<filename>.obj (the extension will depend on your compiler). Each of these files contains a

translation of your source code file into a machine language file -- but you can't run them yet!

You need to turn them into executables your operating system can use. That's where the

linker comes in.

Linking refers to the creation of a single executable file from multiple object files. In this step,

it is common that the linker will complain about undefined functions (commonly, main itself).

During compilation, if the compiler could not find the definition for a particular function, it

would just assume that the function was defined in another file. If this isn't the case, there's no

way the compiler would know -- it doesn't look at the contents of more than one file at a time.

The linker, on the other hand, may look at multiple files and try to find references for the

functions that weren't mentioned.

14.     Diff between local(automatic) & global variables.

The lifetime and scope of local variables is the function or block in which they are declared.

The lifetime and scope of global variables is the program in which they are declared.

15.     How many cases are possible in a select case?

256, range of char.

16.     What is difference between actual and formal parameters?

Actual Parameters :Variables associated with function name during function call statement.

Formal Parameters:Variables which contains copy of actual parameters inside the function definition.

17.     What do you mean by entry controlled and exit controlled loop?

Entry control loop works for true condition and preferred for fixed no.of times.eg for, while

Exit Control Loop execute at least once if the condition is false at beginning.eg do while

18.     Difference between signed and unsigned.

The range of signed data type is lower than unsigned as one byte is reserved to store the sign(-, +)

Eg

 For char datatype.

       1byte signed:    -128 to 127

        unsigned:    0 to 255

19.     What do you understand by .h in header file declarations?

.h stands for header files , an extension given to these type of files.

20.     Why do we use comments? Declare a single line comment and a multi line comment.

Comments are the line that compiler ignores to compile or execute. There are two types of comments in C++.

1.

..Single line comment: This type of comment deactivates only that line where comment is

applied. Single line comments are applied with the help of “ //” .

e.g // cout<<tomorrow is holiday

the above line is proceeding with // so compiler wont access this line.

2. Multi line Comment : This Type of comment deactivates group of lines when applied. This type of comments are applied with the help of the operators “/*” and “*/ ”. These comment mark with /*

and end up with */. This means every thing that falls between /*and */ is considered even though it

is spread across many lines.

e.g #include<iostream.h>

 int main ()

{

 cout<< “ hello world”;

/* this is the program to print hello world

 For demonstration of comments */

}

In the above program the statements between /* and */ will be ignored by the compiler.

21.     Why do we use iostream.h?

To be able to connect the program to the input and output stream.

22.     What is the difference between gets() and getline()?

Gets():It reads up to the '\n' and leaves it in the stream This effectively prevents any further stream processing until the '\n' is cleared with clear() or possibly ignore().

Getline(): It reads up to the '\n' and then discards it.

What type of function is main()- user defined or in-built?

in-built

23.     What happens during running

During running .exe and .bak files are created and the program is loaded in the ram.

24.     Diff. between continue & break & exit

exit()- defined in process.h and used to terminate the program depending upon certain condition.

 break- exit from the current  loop depending upon certain condition.

continue- to skip the remaining statements of the current loop and passes control to the next loop control statement.

25.     What are default arguments?

26.     Function Prototype Function Defintion

Function Header with list of parameters passed , return type mentioned , ended with a ; Must match with Function header of defined body.

Function definition :Function containing body/statements to be executed.

27.     Compile Time Errors: Syntax errors occurs at compile time.

Run Time Errors: Logical Errors occurs at Run Time

28.     Switch Case : Only used with char / int, Only used for equality comparison

29.     If..else:Can be used with all data types, Mix expressions can be evaluated.

30.     What is preprocessor directive?

The preprocessor is used to modify your program according to the preprocessor directives in your source code. Preprocessor directives (such as #define) give the preprocessor specific instructions on how to modify your source code. The preprocessor reads in all of your include files and the source code you are compiling and creates a preprocessed version of your source code. This preprocessed version has all of its macros and constant symbols replaced by their corresponding code and value assignments. If your source code contains any conditional preprocessor directives (such as #if), the preprocessor evaluates the condition and modifies your source code accordingly. The preprocessor contains many features that are powerful to use, such as creating macros, performing conditional compilation, inserting predefined environment variables into your code, and turning compiler features on and off. For the professional programmer, in-depth knowledge of the features efficient programs.