Interview Quesions

Q) what operations can be performed on pointers ?

I said- normal referencing, dereferencing, & normal arithmetic
operations like addition, subtraction, increment, decrement.The
i said- using dereferencing operator one can perform all the
operations allowed on referenced variables, using pointers.
But he said- can u divide pointers?I said- no. He said- then
why did you say so? You are contradicting urself. I don’t know
when did I…

Q) do you know something about call by value & call by reference?
I said yes.He asked me to tell the differnce. i said- If you use
call by value, you create a copy of original object/var. & all the
operations performed modifies only the copy. Original object remains
unchanged.But, If you use call by reference, a reference is created
instead of a copy, & all the operations are reflected in original
object.

Q) so if you want to change the value, would you use a function or
a procedure?
I said - a procedure.He asked me- why?I said- convetionally,function
is used when we wan’t to return a value such as a status info.or
result of any operation. Then I said- since a procedure does not
return any value to point of reference (where it was called) only
the referenced values are manipulated.He said- Now,you are saying
that procedure doesn’t return a value so u r contradicting urself
for ur using procedure to change a value.I said- no,a function is
used when we want to return a value to point of reference,It can
return only a single value.& original vals. are not modified unless
they use the return value of the function (i.e.,by appearing on the
L.H.S. of an assignment including a function call.)

Q) what does a function returns?
I said- any return value, that we want it return. Like result of
an operation. He asked- explain.Like if you want to add two values,
then what would the function return? I said- ok,if you are using a
function sum like (i wrote it on a paper) int sum (int a, int b)
{ return a+b; } & calling the function like c = sum(a,b); then the
function sum will return the value of operation a+b to c.

Q) int i=0; while(i=0) printf(”%d”,++i); Guess the output *****
infinite loop

Q) int x=2, y=6, z=6; x=y==z; printf(”%d”,x); Guess the output *****
prints 1.

Q. What is a configuration file?
A. A configuration file tells Turbo C++ what options to default to
and where to look for its library and header files.TC.EXE looks for
a configuration file named TCCONFIG.TC, and TCC.EXE looks for a file
named TURBOC.CFG.

When linking C or Assembly language modules with C++ modules I get
undefined symbol errors at link time.It appears that none of the C
or Assembly public symbols can be found.
A.C++ is a strongly typed language.In order to support the language
to its fullest, Turbo C++ must attach information to the symbols
generated for function names and variables. When this is done,
the symbol will no longer match the standard C style function name.
In order to link correctly, the compiler must be notified that the
symbol is declared in an external module without type information
tacked on to the symbol. This is done by prototyping the function
as type extern “C”.Here is a quick example:
                extern “C” int normal_c_func( float, int, char );
// name not altered void cplusplus_function( int );
// name altered See related comments under Linker Errors and in
the Paradox Engine question in this section.

Classes with static data members are getting linker errors
(”undefined”).
A. This code is built into Turbo C++ 1.0 but not in version 3.0.
In the 1.0 compiler,static members without definitions were given
a default value of 0.This default definition will no longer be made
in the compiler.The programmer must now give an explicit definition
for each static member.Here is a quick example:
class A { static int i; }; A linker error saying that A::i is not
defined will result unless the source also contains a line such as:
int A::i = 1;

What potential problems can arise from typecasting a base class
pointer into a derived class pointer so that the derived class’s
member functions can be called?
A.Syntactically this is allowable. There is always the possibility
of a base pointer actually pointing to a base class. If this is
typecast to a derived type, the method being called may not exist
in the base class. Therefore, you would be grabbing the address of
a function that does not exist.

Q: What’s the difference between the keywords STRUCT and CLASS?
A: The members of a STRUCT are PUBLIC by default, while in CLASS,
 they default to PRIVATE. They are otherwise functionally equivalent.

Q: I have declared a derived class from a base class, but I can’t
access any of the base class members with the derived class function.
A: Derived classes DO NOT get access to private members of a base
class. In order to access members of a base class, the base class
members must be declared as either public or protected. If they are
public, then any portion of the program can access them.If they are
protected,they are accessible by the class members,friends, and any
derived classes.

Q: How can I use the Paradox Engine 1.0 with C++?,
A: Because the Paradox Engine functions are all compiled as C
functions, you will have to assure that the names of the functions
do not get “mangled” by the C++ compiler. To do this you need to
prototype the Engine functions as extern “C”. In the pxengine.h
header file insert the following code at the lines indicated.
 /* inserted at line # 268 */ #ifdef __cplusplus extern “C”
{ #endif /* inserted at line # 732, just before the final #endif */
 #ifdef __cplusplus } #endif Paradox Engine version 2.0 is “aware”
of C++ and thus does not require any modifications to its header file.
 

I have a class that is derived from three base classes. Can I insure
that one base class constructor will be called before all other
constructors?
A: If you declare the base class as a virtual base class, its
constructor will be called before any non-virtual base class
constructors.Otherwise the constructors are called in left-to-right
order on the declaration line for the class.

Q: Are the standard library I/O functions still available for
use with the C++ iostreams library?
A: Yes, using #include functions such as printf() and scanf() will
continue to be available. However, using them in conjunction with
stream oriented functions can lead to unpredictable behaviour.

Q: In C++, given two variables of the same name, one local and one
global, how do I access the global instance within the local scope?
A.Use the scope (::) operator. int x = 10; for(int x=0; x < ::x; x++)
 { cout << “Loop # ” << x << “\n”; // This will loop 10 times }

Q: Will the following two functions be overloaded by the compiler,
or will the compiler flag it as an error? Why?

void test( int x, double y); & int test( int a, double b); A. The
compiler will flag this as a redeclaration error because neither
return types nor argument names are considered when determining
unique signatures for overloading functions. Only number and type
of arguments are considered.

Q: If I pass a character to a function which only accepts an int,
what will the compiler do? Will it flag it as an error?
A. No. The compiler will promote the char to an int and use the
integer representation in the function instead of the character
itself.

Q: I was trying to allocate an array of function pointers using the
new operator but I keep getting declaration syntax errors using the
following syntax: new int(*[10])(); What’s wrong?
A. The new operator is a unary operator and binds first to the int
keyword producing the following: (new int) (*[10])(); You need to
put parentheses around the expression to produce the expected results:
 new (int (*[10]());

Q: What are inline functions? What are their advantages? How are
they declared?
A. An inline function is a function which gets textually inserted
by the compiler, much like macros. The advantage is that execution
time is shortened because linker overhead is minimized. They are
declared by using the inline keyword when the function is declared:
inline void func(void) { cout << “printing inline function \n”; } or
by including the function declaration and code body within a class:
class test { public: void func(void) { cout << “inline function within
 a class.\n”} };

Q: If I don’t specify either public or private sections in a class,
what is the default? A. In a class, all members are private by default
if neither public nor private sections are declared.

Q: What is a friend member function?
A. Declaring a friend gives non-members of a class access to the
non-public members of a class.

Q: Why do I get a “Type name expected” error on my definition of a
friend class in my new class?
A You need to let the compiler know that the label you use for your
friend class is another class.If you do not want to define your entire
class, you can simply have “class xxx”, where xxx is your label.

Q: What is the “this” pointer?
A. “this” is a local variable in the body of a non-static member
function. It is a pointer to the object for which the function was
invoked. It cannot be used outside of a class member function body.

Q: Why does a binary member function only accept a single argument?
A. The first argument is defined implicitly.

Q: Looking through the class libraries there are definitions in
classes which look like: class test { int funct( void ) const; };
What is the const keyword doing here?
A. There is a pointer to the object for which a function is called
known as the ‘this’ pointer. By default the type of ‘this’ is
X *const ( a constant pointer). The const keyword changes the type
to const X *const ( a constant pointer to constant data ).

I would like to use C++ fstreams on a file opened in binary mode,
how is this done?
A: Use ios::binary as the open mode for the file: #include ifstream
binfile; binfile.open(”myfile.bin”, ios::binary);

Q: How can I find out where my “null pointer assignment” is
occurring?
A. Set a watch on the following expressions:
*(char *)0,4m (char *)4 Step through the program. When the values
change,the just-executed line is the one that is causing the problem.
Null pointer is known not to point to any object; an uninitialized
pointer might point anywhere.there is a null pointer for each pointer
type,and the internal values of null pointers for different types may
be different. And is implicitly defined as : preprocessor macro NULL
is #defined (by or ), with value 0

Q: When I try to load a new file after editing a file, the first file
remains on the screen. How do I close the first file?
A. Use Alt-F3 to close the current file.Also, use F6 to move from one
file to the next, if there is more than one file open at a time.

Q: I’m doing a search and replace operation, and the editor prompts
me for each replacement. I’ve selected “Change All”, but it still
does it.
A. To disable the prompting,you must unselect the “Prompt on replace”
option on the left side of the dialog box.

Q: When I try to use the any of the pseudo registers, like _AX, I get
the error message “Undefined symbol ‘_AX’ in function…” when I
compile. Why?
A. You are only allowed to use the pseudo registers in the Turbo C++
and ANSI modes of the compiler. You can change this setting in the
Options | Compiler | Source menu.

Q: Since I don’t have a mouse, can I still copy blocks of code from
one file to another?
A. Yes. You can mark the beginning and end of a block by moving to
the appropriate area and pressing Ctrl-K-B (mark beginning) and
Ctrl-K-K (mark end). You can then use the copy and paste commands
in the Edit menu.

Q:How do I stop all of the files I have ever edited from constantly
being open when I bring up Turbo C++?
A: BY default, Turbo C++ saves what is called the desktop
configuration. This configuration is saved in a file with a .DSK
extension. By deleting any files of this type, then entering
Options/Environment/Preferences and removing the check from ‘auto
save desktop’, you will begin with a clean desktop each time you
invoke Turbo C++.

Q: The ‘\n’ in cprintf() does not return the cursor to the beginning
of the line. It only moves the cursor down one line.
A. cprintf() interprets ‘\n’ as a Line Feed. To force the cursor to
the beginning of the line, manually insert a Carriage
Return: cprintf(”\n\r”);

Q: How do I print to the printer from a Turbo C++ program?
A. Turbo C++ uses a FILE pointer (stdprn) defined in the STDIO.H
file. You do not need to open stdprn before using it: #include int
main(void) { fprintf(stdprn, “Hello, printer!\n”); } Note that if
your printer is line-buffered, the output is flushed only after a
‘\n’ is sent.

Q: Why don’t printf() and puts() print text in color?
A. Use the console I/O functions cprintf() and cputs() for color
output.
#include int main(void) { textcolor(BLUE); cprintf(”I’m blue.”); }

Q: How do I print a long integer?
A. Use the “%ld” format: long int l = 70000L; printf(”%ld”, l);

Q: How do I print a long double?
A. Use the “%Lf” format. long double ldbl = 1E500;
printf(”%Lf”, ldbl);

Q: How do I compile the BGIDEMO program?
A. 1. Make sure that the following Turbo C++ files are in your
current directory: BGIDEMO.C *.BGI *.CHR 2. Run Turbo C++. 3.
Load BGIDEMO.C into the Editor by pressing F3,then typing BGIDEMO 3.
Go to the Run menu and choose the Run item.

Q: How do I create a COM file?
A. DOS versions 3.2 and earlier include an EXE2BIN utility that
converts EXE files to COM files. Users who do not have EXE2BIN can
use TLINK, the Turbo C++ command-line linker, to create a COM file instead of an EXE file. Use the /t option. For example: TCC -mt -lt tiny will create TINY.COM instead of TINY.EXE. The -l switch passes the /t argument to the linker in this case.

Q: Why do I get incorrect results from all the math library functions
like cos(), tan() and atof()?
A. You must #include before you call any of the standard Turbo C++
math functions. In general, Turbo C++ assumes that a function that is
not declared returns an int.In the case of math functions.they usually
 return a double. For example
/* WRONG */ /* RIGHT */ #include int main(void) int main(void) {
{ printf(”%f”, cos(0)); printf(”%f”, cos(0)); } }

Q: How do I change the stack size?
A. The size of the stack of a Turbo C++ program is determined at run
time by the global variable _stklen. To change the size to, for
example, 10,000 bytes, include the following line in your program:
extern unsigned _stklen = 10000; This statement must not be inside
any function definition. The default stack size is 4,096 bytes (4K).

Q: My program comes up with the message ‘Null pointer assignment’
after it terminates. What does this mean?
A. Before a small-data model Turbo C++ program returns to DOS, it
will check to see if the beginning of its data segment has been
corrupted. This message is to warn you that you have used
uninitialized pointers or that your program has corrupted memory
in some other way.

Q: Why are .EXE files generated by TC.EXE larger than those generated
 by TCC.EXE?
A. In the default configuration, TC.EXE includes debugging
information in the .EXE files that it creates, and TCC.EXE does
not. If you don’t want to produce this debugging information,
you can shut it off in the Integrated Development Environment by
selecting Alt-O|B|N.

Q: I have a working program that dynamically allocates memory using
malloc() or calloc() in small data models (tiny, small, and medium).
When I compile this program in large data models (compact, large, and
huge), my program hangs.
A. Make sure that you have #include in your program.

Q) I had definition char x[6] in one source file, and another I
declared extern char *x. Why didn’t it work?
Ans) The declaration extern char *x simply does not match the actual
definition. The type “pointer-to-type-T” is not the same as
“array-of-type-T.” Use extern char x[]. But I heard that char x[] was
 identical to char *x. But it is wrong.