Posts
1.What
is C language?
Ans:
The C programming language is a standardized
programming language developed in the
early 1970s by Ken Thompson and Dennis Ritchie for use on the
UNIX operating system. It has since spread to many other operating systems, and
is one of the most widely used programming languages. C is prized for its
efficiency, and is the most popular programming language for writing system
software, though it is also used for writing applications.
2.What does static
variable mean?
Ans:
Static variables are the variables which retain their values between the
function calls. They are initialized only once their scope is within the
function in which they are defined.
3.What is a pointer?
Ans:
Pointers are variables which stores the address of another variable. That
variable may be a scalar (including another pointer), or an aggregate
(array or structure). The pointed- to object may be part of a larger object,
such as a field of a structure or an element in an array.
4.What are the uses
of a pointer?
Ans: Pointer is used in
the following cases
i) It is used to access
array elements
ii) It is used for
dynamic memory allocation.
iii) It is used in Call by
reference
iv) It is used in data
structures like trees, graph, linked list etc.
5.What
are the pointer declarations used in C? Ans:
1- Array of pointers, e.g , int
*a[10]; Array of pointers to integer 2-Pointers to an array,e.g , int (*a)[10];
Pointer to an array of into
3-Function returning
a pointer,e.g, float *f( ) ; Function returning a pointer to float 4-Pointer to
a pointer ,e.g, int **x; Pointer to apointer to int
5-pointer to a data
type ,e.g, char *p; pointer to char
6.What
is Polymorphism ?
Ans: 'Polymorphism' is an object oriented term. Polymorphism
may be defined as the ability of related
objects to respond to the same message with different, but appropriate actions.
In other words,
polymorphism
means taking more than one form. Polymorphism leads to two important aspects in
Object Oriented terminology – Function Overloading and Function Overriding.
Overloading is the practice of supplying more than one
definition for a given function name in the same scope. The compiler is left to
pick the appropriate version of the function or operator based on the arguments
with which it is called. Overriding refers to the modifications made in the sub
class to the inherited methods from the base class to change their behavior.
7.What is a
structure?
Ans:
Structure constitutes a super data type which represents several different data
types in a single unit. A structure can be initialized if it is static or
global.
8.What is a union?
Ans:
Union is a collection of heterogeneous data type but it uses efficient memory
utilization technique by allocating enough memory to hold the largest
member. Here a single area of memory contains values of different types at
different time. A union can never be initialized.
9.What are the
differences between structures and union?
Ans: A
structure variable contains each of the named members, and its size is large
enough to hold all the members. Structure elements are of same size.
A
union contains one of the named members at a given time and is large enough to
hold the largest member. Union element can be of different sizes.
10.What are the
differences between structures and arrays?
Ans: Structure is a
collection of heterogeneous data type but array is a collection of homogeneous
data types.
Array
1-It is a collection
of data items of same data type. 2-It has declaration only
3-.There is no
keyword.
4-
array name represent the address of the starting element.
Structure
1-It is a collection
of data items of different data type. 2- It has declaration and definition
3- keyword struct is
used
4-Structure name is
known as tag it is the short hand notation of the declaration.
11.How
are pointer variables initialized?
Ans: Pointer variable are
initialized by one of the following two ways
- Static
memory allocation
- Dynamic
memory allocation
12.Difference
between arrays and pointers?
Ans:
- Pointers are used to manipulate data using the address.
Pointers use * operator to
access the data pointed to by them
-
Arrays use subscripted variables to access and manipulate data.
Array
variables can be equivalently written using pointer expression.
13.Is
using exit() the same as using return?
Ans: No. The exit()
function is used to exit your program and return control to the operating system. The return statement is used to return from a
function and return control to the calling function. If you issue a return from
the main() function, you are essentially returning control to the calling
function, which is the operating system. In this case, the return statement and
exit() function are similar.
14.What
is a method?
Ans:
Method is a way of doing something, especially a systematic way;
implies an orderly logical
arrangement (usually in steps).
15.What
is indirection?
Ans:
If you declare a variable, its name is a direct reference to its
value. If you have a pointer to a
variable, or any other object in memory, you have an indirect reference to its
value.
16.Why
should I prototype a function?
Ans:
A function prototype tells the compiler what kind of arguments a
function is looking to receive and
what kind of return value a function is going to give back. This approach helps
the compiler ensure that calls to a function are made correctly and that no
erroneous type conversions are taking place.
17.What
is static memory allocation and dynamic memory allocation?
Ans: Static
memory allocation: The compiler allocates
the required memory space for a declared variable.By using the address of operator,the reserved
address is obtained and this address may be assigned to a pointer
variable.Since most of the declared variable have static
memory,this way of assigning pointer value to a pointer variable
is known as static memory allocation. memory is assigned during compilation
time.
Dynamic memory allocation: It uses
functions such as malloc( ) or calloc( ) to get memory dynamically.If
these functions are used to get memory dynamically and the values returned by
these functions are assingned to pointer variables, such assignments are known
as dynamic memory allocation.memory is assined during run time.
18.Difference between
an array of pointers and a pointer to an array? Ans:
Array of pointers
1- Declaration is:
data_type *array_name[size];
2-Size represents the
row size.
3- The space for
columns may be dynamically
Pointers to an array
1-Declaration is
data_type ( *array_name)[size];
2-Size represents the
column size.
19.What are the differences between malloc() and calloc()? Ans: There are 2 differences.
First, is in the number of arguments. malloc() takes a single
argument(memory required in bytes), while calloc() needs 2 arguments(number of
variables to allocate memory, size in bytes of a single variable).
Secondly, malloc() does not initialize the memory allocated,
while calloc() initializes the allocated memory to ZERO.
20.malloc()
Function- What is the difference between "calloc(...)" and
"malloc(...)"? Ans:
1. calloc(...)
allocates a block of memory for an array of elements of a certain size. By
default the block is initialized to 0. The total number of memory allocated
will be (number_of_elements * size). malloc(...) takes in only a single
argument which is the memory required in bytes. malloc(...) allocated bytes of
memory and not blocks of memory like calloc(...).
2. malloc(...) allocates memory blocks and returns a void
pointer to the allocated space, or NULL if there is insufficient memory
available. calloc(...) allocates an array in memory with elements initialized
to 0 and returns a pointer to the allocated space. calloc(...) calls
malloc(...) in order to use the C++ _set_new_mode function to set the new
handler mode.
21.printf() Function- What is the difference between
"printf(...
|
)" and "sprintf(...
|
)"?
|
|
Ans: sprintf(...
|
) writes data to the character array whereas printf(...
|
) writes data to the
|
|
standard
output device.
|
|||
22.Compilation
How to reduce a final size of executable?
Size of
the final executable can be reduced using dynamic linking for libraries.
23.How
would you use the functions fseek(), freed(), fwrite() and ftell()? Ans:
fseek(f,1,i)
Move the pointer for file f a distance 1 byte from location i. fread(s,i1,i2,f)
Enter i2 dataitems,each of size i1 bytes,from file f to string s.
fwrite(s,i1,i2,f) send i2 data items,each of size i1 bytes from string s to
file f. ftell(f) Return the current pointer position within file f.
The data type
returned for functions fread,fseek and fwrite is int and ftell is long int.
24.What is the
difference between the functions memmove() and memcpy()?
Ans:
The
arguments of memmove() can overlap in memory. The arguments of memcpy() cannot.
25.What is a file?
Ans:
A
file is a region of storage in hard disks or in auxiliary storage devices.It
contains bytes of
information .It is
not a data type.
26.IMP>what are
the types of file?
Ans: Files are of two
types
1-high
level files (stream oriented files) :These files are accessed using library
functions 2-low level files(system oriented files) :These files are accessed
using system calls
27.IMP>what is a
stream?
Ans: A stream is a source of data
or destination of data that may be associated with a disk or other I/O
device. The source stream provides data to a program and it is known as input
stream. The destination stream eceives the output from the program and is known
as output stream.
28.What is meant by
file opening?
Ans: The action of connecting a
program to a file is called opening of a file. This requires creating an
I/O stream before reading or writing the data.
29.What is FILE?
Ans: FILE is a predefined
data type. It is defined in stdio.h file.
30.What
is a null pointer?
Ans:
There are times when it’s necessary to have a pointer that
doesn’t point to anything. The macro
NULL, defined in , has a value that’s guaranteed to be different from any valid
pointer. NULL is a literal zero, possibly cast to void* or char*. Some people,
notably C++ programmers, prefer to use 0 rather than NULL.
The
null pointer is used in three ways:
1) To stop
indirection in a recursive data structure
2) As an
error value
3)
As a sentinel value
31.In header files
whether functions are declared or defined?
Ans:
Functions
are declared within header file. That is function prototypes exist in a header
file,not function bodies. They are defined in library (lib).
32.What are the
differences between malloc () and calloc ()?
Ans:
Malloc
Calloc 1-Malloc takes one argument Malloc(a);where a number of bytes 2-memory
allocated contains garbage values
1-Calloc
takes two arguments Calloc(b,c) where b no of object and c size of object 2-It
initializes the contains of block of memory to zerosMalloc takes one argument,
memory allocated contains garbage values.
It
allocates contiguous memory locations. Calloc takes two arguments, memory
allocated contains all zeros, and the memory allocated is not contiguous.
33.What
are macros? What are its advantages and disadvantages? Ans: Macros
are abbreviations for lengthy and frequently used statements. When a macro is
called the entire code is substituted by a single line though the macro
definition is of several lines. The advantage of macro is that it
reduces the time taken for control transfer as in case of
function. The disadvantage of it is here the
entire code is substituted so the program becomes
lengthy if a macro is
called several times.
34.Difference between
pass by reference and pass by value?
Ans:
Pass
by reference passes a pointer to the value. This allows the callee to modify
the variable directly.Pass by value gives a copy of the value to the
callee. This allows the callee to modify the value without modifying the
variable. (In other words, the callee simply cannot modify the variable, since
it lacks a reference to it.)
35.What is static
identifier?
Ans:
A
file-scope variable that is declared static is visible only to functions within
that file. A
function-scope
or block-scope variable that is declared as static is visible only within that
scope. Furthermore, static variables only have a single instance. In the case
of function-or block-scope variables, this means that the variable is not
“automatic” and thus retains its value across function invocations.
36.What
are the different storage classes in C?
Ans: C has
three types of storage: automatic, static and allocated.
Variable
having block scope and without static specifier have automatic storage
duration. Variables with block scope, and with static specifier have static
scope.
Global variables (i.e, file scope) with or without the static
specifier also have static scope. Memory obtained from calls to malloc(),
alloc() or realloc() belongs to allocated storage class
37.Where is the auto
variables stored?
Ans:
Auto
variables can be stored anywhere, so long as recursion works. Practically, they’re
stored on the stack. It is not necessary that always a stack exist. You could
theoretically allocate function invocation records from the heap.
38.Where does global,
static, and local, register variables, free memory and C Program instructions
get stored?
Ans:
Global:
Wherever the linker puts them. Typically the “BSS segment” on many platforms.
Static: Again, wherever the linker
puts them. Often, they’re intermixed with the globals. The only difference
between globals and statics is whether the linker will resolve the symbols
across compilation units.Local: Typically on the stack, unless the variable
gets register allocated and never spills.Register: Nowadays, these are
equivalent to “Local” variables. They live on the stack unless they get
register-allocated.
39.Difference between
arrays and linked list?
Ans:
An
array is a repeated pattern of variables in contiguous storage. A linked list
is a set of
structures scattered through memory,
held together by pointers in each element that point to the next element. With
an array, we can (on most architectures) move from one
element
to the next by adding a fixed constant to the integer value of the pointer.
With a linked list, there is a “next” pointer in each structure which says what
element comes next.
40.What are
enumerations?
Ans:
They
are a list of named integer-valued constants. Example:enum color { black , orange=4,
yellow,
green, blue, violet };This declaration defines the symbols “black”, “orange”,
“yellow”, etc. to have the values “1,” “4,” “5,” … etc. The difference between
an enumeration and a macro is that the enum actually declares a type, and
therefore can be type checked.
50.What
is the difference between strings and character arrays?
Ans: A major
difference is: string will have static storage duration, whereas as a character array will not, unless it is explicity specified by using the
static keyword.
Actually,
a string is a character array with following properties:
*
the multibyte character sequence, to which we generally call
string, is used to initialize an array of static storage duration. The size of
this array is just sufficient to contain these characters plus the terminating
NUL
character.
* it not
specified what happens if this array, i.e., string, is modified.
* Two
strings of same value[1] may share same memory area. For
example, in the
following declarations: char *s1 = “Calvin and Hobbes”;
char
*s2 = “Calvin and Hobbes”;
the
strings pointed by s1 and s2 may reside in the same memory location. But, it is
not true for the following:
char ca1[] = “Calvin and
Hobbes”; char ca2[] = “Calvin and Hobbes”;
[1] The value of a string is the sequence of the values of the
contained characters, in order.
51.Describe about
storage allocation and scope of global, extern, static, local and register
variables?
Ans:
Globals
have
application-scope. They’re available in any compilation unit that includes an
appropriate
declaration (usually brought from a header file). They’re stored wherever the
linker puts them, usually a place called the “BSS segment.”
Extern?
This is essentially “global.”
Static:
a
variable known only in function . Stored the same place as globals,
typically, but only available to the compilation unit that contains
them. If they are block-scope global, only available within that block and its
subblocks.
Local: Stored on the stack, typically.
Only available in that block and its subblocks. (Although pointers to
locals can be passed to functions invoked from within a scope where that local
is valid.)
Register: A type of auto variable. “local” vs.
“register.” The only difference is that the C compiler will not let you
take the address of something you’ve declared as “register.”
52.What are register variables? What are the
advantages of using register variables? Ans: If a variable is
declared with a register storage class,it is known as register variable.The
register variable is
stored in the cpu register instead of main memory.Frequently used variables
are declared as
register variable as it’s access time is faster.
53.What is the use of
typedef?
Ans:
The
typedef help in easier modification when the programs are ported to another machine.
A
descriptive new name given to the existing data type may be easier to
understand the code.
54.Can we specify variable field width in a
scanf() format string? If possible how? Ans: All field widths
are variable with scanf(). You can specify a maximum field width for a
given field by placing an integer value between the ‘%’ and the field type
specifier. (e.g. %64s). Such a specifier will still accept a narrower field width.
The one exception is %#c (where # is an integer). This
reads EXACTLY # characters, and it is the only way to specify a fixed field
width with scanf().
55.Out of fgets() and
gets() which function is safe to use and why?
Ans:
fgets()
is safer than gets(), because we can specify a maximum input length. Neither
one is completely safe, because the compiler can’t prove that programmer
won’t overflow the buffer he pass to fgets ().
56.What is a modulus operator? What are the restrictions of a modulus
operator?
A Modulus operator gives the remainder value. The result of x%y
is obtained by (x-(x/y)*y). This operator is applied only to integral operands
and cannot be applied to float or double.
57.Difference between
strdup and strcpy?
Ans:
Both
copy a string. strcpy wants a buffer to copy into. strdup allocates a buffer
using malloc().
Unlike strcpy(),
strdup() is not specified by ANSI .
58.What is recursion?
Ans:
A
recursion function is one which calls itself either directly or indirectly it
must halt at a definite point to avoid infinite recursion.
59.Differentiate
between for loop and a while loop? What are it uses?
Ans: For executing a set
of statements fixed number of times we use for loop while when
the number of
iterations to be performed is not known in advance we use while loop.
60.What is storage
class? What are the different storage classes in C?
Ans: Storage class is an
attribute that changes the behavior of a variable. It controls the lifetime,
scope and linkage. The storage classes in c are auto, register, and extern,
static, typedef.
61.What the
advantages of using Unions?
Ans: When the C compiler is
allocating memory for unions it will always reserve enough room for the
largest member.
62.What is the
difference between Strings and Arrays?
Ans:
String
is a sequence of characters ending with NULL .it can be treated as a one dimensional
array of characters terminated by a NULL character.
63.What is a far
pointer? Where we use it?
Ans: In large data model (compact, large,
huge) the address B0008000 is acceptable because in these model all
pointers to data are 32bits long. If we use small data model(tiny, small,
medium) the above address won’t work since in these model each pointer is
16bits long. If we are working in a small data model and want to access the address
B0008000 then we use far pointer. Far pointer is always treated as a 32bit
pointer and contains a segment address and offset address both of 16bits each.
Thus the address is represented using segment : offset format B000h:8000h. For
any given memory address there are many possible far address segment : offset
pair. The segment register contains the address where the segment begins and
offset register contains the offset of data/code from where segment begins.
64.What is a huge
pointer?
Ans: Huge pointer is 32bit long containing
segment address and offset address. Huge pointers are normalized
pointers so for any given memory address there is only one possible huge
address segment: offset pair. Huge pointer arithmetic is doe with calls to
special subroutines so its arithmetic slower than any other pointers.
65.What is a
normalized pointer, how do we normalize a pointer?
Ans: It is a 32bit pointer, which has as
much of its value in the segment register as possible. Since a segment
can start every 16bytes so the offset will have a value from 0 to F. for
normalization convert the address into 20bit address then use the 16bit for
segment address and 4bit for the offset address. Given a pointer 500D: 9407,we
convert it to a 20bitabsolute address 549D7,Which then normalized to 549D:0007.
66.What is near
pointer?
Ans:
A
near pointer is 16 bits long. It uses the current content of the CS (code
segment) register (if the pointer is pointing to code) or current
contents of DS (data segment) register (if the pointer is pointing to data) for
the segment part, the offset part is stored in a 16 bit near pointer. Using
near pointer limits the data/code to 64kb segment.
67.In C, why is the
void pointer useful? When would you use it?
Ans:
The
void pointer is useful because it is a generic pointer that any pointer can be
cast into and back again without loss of information.
68.What is a NULL
Pointer? Whether it is same as an uninitialized pointer?
Ans:
Null
pointer is a pointer which points to nothing but uninitialized pointer may
point to anywhere.
69.Are pointers
integer?
Ans: No, pointers are not
integers. A pointer is an address. It is a positive number.
70.What does the
error ‘Null Pointer Assignment’ means and what causes this error?
Ans:
As
null pointer points to nothing so accessing a uninitialized pointer or invalid
location may cause an error.
71.Difference
between const char* p and char const* p
Ans: In const char* p, the
character pointed by ‘p’ is constant, so u cant change the value of character pointed by p but u can make
‘p’ refer to some other location. in char const* p, the ptr ‘p’ is constant not
the character referenced by it, so u cant make ‘p’ to reference to any other
location but u can change the value of the char pointed by ‘p’.
72.What
is hashing?
Ans: To hash means
to grind up, and that’s essentially what hashing is all about. The heart of a hashing algorithm is a hash function that takes your
nice, neat data and grinds it into some random-looking integer. The idea behind
hashing is that some data either has no inherent
ordering
(such as images) or is expensive to compare (such as images). If the data has
no inherent ordering, you can’t perform comparison searches.
If the
data is expensive to compare, the number of comparisons used even by a binary
search might be too many. So instead of looking at the data themselves, you’ll
condense (hash) the data to an integer (its hash value) and keep all the data
with the same hash value in the same place. This task is carried out by using
the hash value as an index into an array.
To
search for an item, you simply hash it and look at all the data whose hash
values match that of the data you’re looking for. This technique greatly
lessens the number of items you have to look at. If the parameters are set up
with care and enough storage is available for the hash table, the number of
comparisons needed to find an item can be made arbitrarily close to one.
One
aspect that affects the efficiency of a hashing implementation is the hash
function itself. It should ideally distribute data randomly throughout the
entire hash table, to reduce the likelihood of collisions.
Collisions occur when two
different keys have the same hash value. There are two ways to resolve this
problem. In open addressing, the collision is resolved by the choosing of
another position in the hash table for the element inserted later. When the
hash table is
searched,
if
the entry is not found
at its hashed position in the table, the search continues checking until either
the element is found or an empty position in the table is found.
The second method of resolving a hash collision is called
chaining. In this method, a bucket or linked list holds all the elements whose
keys hash to the same value. When the hash table is searched, the list must be
searched linearly.
73.How
can you determine the size of an allocated portion of memory?
Ans: You can’t,
really. free() can , but there’s no way for your program to know the trick free() uses. Even if you disassemble the library and discover
the trick, there’s no guarantee the trick won’t change with the next release of
the compiler
74.What is generic
pointer in C?
Ans: In C void* acts as a generic pointer.
When other pointer types are assigned to generic pointer, conversions
are applied automatically (implicit conversion).
75.Are
the expressions arr and &arr same for an array of integers? Ans: Yes
for array of integers they are same.
76.What
is Operator overloading ?
Ans:
When an operator is overloaded, it takes on an additional
meaning relative to a certain class.
But it can still retain all of its old meanings.
Examples:
1) The
operators >> and << may be used for I/O operations because in the
header, they are overloaded.
2) In a stack class it is possible to overload the + operator so
that it appends the contents of one stack to the contents of another. But the+
operator still retains its original meaning relative to other types of data.
77.IMP>How pointer
variables are initialized?
Ans:
Pointer
variables are initialized by one of the following ways. I. Static memory
allocation
II. Dynamic memory
allocation
78.What is static
memory allocation?
Ans:
Compiler
allocates memory space for a declared variable. By using the address of operator,
the reserved address is obtained and this address is assigned to a pointer
variable. This way of assigning pointer value to a pointer variable at
compilation time is known as static memory allocation.
79.What is dynamic
memory allocation?
Ans: A dynamic memory allocation uses
functions such as malloc() or calloc() to get memory dynamically. If
these functions are used to get memory dynamically and the values returned by
these function are assigned to pointer variables, such a way of allocating memory
at run time is known as dynamic memory allocation.
80.What is the
purpose of realloc?
Ans:
It
increases or decreases the size of dynamically allocated array. The function
realloc (ptr,n) uses two arguments. The first argument ptr is a pointer to
a block of memory for which the size is to be altered. The second argument
specifies the new size. The size may be increased or decreased. If sufficient
space is not available to the old region the function may create a new region.
81.What is pointer to
a pointer?
Ans:
If
a pointer variable points another pointer value. Such a situation is known as a
pointer to a pointer.
Example:
int
*p1,**p2,v=10; P1=&v; p2=&p1;
Here p2 is a pointer
to a pointer.
82.What is an array
of pointers?
Ans: if the elements of an
array are addresses, such an array is called an array of pointers.
83.Difference between
linker and linkage?
Ans: Linker converts an object
code into an executable code by linking together the necessary built in
functions. The form and place of declaration where the variable is declared in
a program determine the linkage of variable.
84.Is it possible to
have negative index in an array?
Ans: Yes it is possible to index with
negative value provided there are data stored in this location. Even if
it is illegal to refer to the elements that are out of array bounds, the
compiler will not produce error because C has no check on the bounds of an
array.
85.Why
is it necessary to give the size of an array in an array declaration? Ans: When
an array is declared, the compiler allocates a base address and reserves
enough
space in memory for all the elements of the array. The size is required to
allocate the required space and hence size must be mentioned.
86.What modular
programming?
Ans:
If
a program is large, it is subdivided into a number of smaller programs that are
called modules or subprograms. If a complex problem is solved using more
modules, this approach is known as modular programming.
87.What is a
function?
Ans: A large program is
subdivided into a number of smaller programs or subprograms. Each
subprogram specifies one or more actions to be performed for the larger
program. Such sub programs are called functions.
88.What is an
argument?
Ans: An argument is an entity used to pass
data from the calling to a called function.
89.What are built in
functions?
Ans:
The
functions that are predefined and supplied along with the compiler are known
as built-in functions. They are also known as library functions.
90.What is a
preprocessor, what are the advantages of preprocessor?
Ans:
A
preprocessor processes the source code program before it passes through the compiler.
1- a preprocessor
involves the readability of program
2- It facilitates
easier modification
3- It helps in
writing portable programs
4- It enables easier
debugging
5- It enables testing
a part of program
6- It helps in
developing generalized program
91.What
are the facilities provided by preprocessor? Ans:
1-file inclusion
2-substitution
facility
3-conditional
compilation
92.Write a program
to interchange 2 variables without using the third one.
Ans:
a ^=
b; ie a=a^b b ^= a; ie b=b^a; a ^= b ie a=a^b;
here the numbers are converted into
binary and then xor operation is performed. You know, you’re just asking “have
you seen this overly clever trick that’s not worth applying onmodern
architectures and only really applies to integer variables?”
93.IMP>what are C
tokens?
Ans:
There
are six classes of tokens: identifier, keywords, constants, string literals,
operators and other separators.
94.What are C
identifiers?
Ans: These are names given to
various programming element such as variables, function, arrays.It is a
combination of letter, digit and underscore.It should begin with letter.
Backspace is not allowed.
95.Difference between
syntax vs logical error? Ans:
Syntax Error
1-These involves
validation of syntax of language.
2-compiler prints diagnostic
message.
Logical Error
1-logical error are
caused by an incorrect algorithm or by a statement mistyped in such a way
that
it doesn’t violet syntax of language. 2-difficult to find.
96.What is
preincrement and post increment?
Ans:
++n
(pre increment) increments n before its value is used in an assignment operation
or any
expression containing
it. n++ (post increment) does increment after the value of n is used.
97.What is a file
pointer?
Ans: The pointer to a FILE data type is
called as a stream pointer or a file pointer. A file pointer points to
the block of information of the stream that had just been opened.
98.How is fopen()used
?
Ans:
The
function fopen() returns a file pointer. Hence a file pointer is declared and
it is assigned
as
FILE *fp;
fp=
fopen(filename,mode);
filename is a string
representing the name of the file and the mode represents: “r” for read
operation
“w” for write operation “a” for append
operation
“r+”,”w+”,”a+” for
update operation
99.What
is the difference between goto and longjmp() and setjmp()?
Ans:
A goto statement implements a local jump of program execution,
and the longjmp()
and setjmp() functions implement a nonlocal, or far, jump of
program execution. Generally, a jump in execution of any kind should be avoided
because it is not considered good programming practice to use such statements
as goto and longjmp in your program. A goto statement simply bypasses code in
your program and jumps to a predefined position. To use the goto statement, you
give it a labeled position to jump to. This predefined position must be within
the same function. You cannot implement gotos between functions.
When your program calls setjmp(), the current state of your
program is saved in a structure of type jmp_buf. Later, your program can call
the longjmp() function to restore the program’s state as it was when you called
setjmp().Unlike the goto statement, the longjmp() and setjmp() functions do not
need to be implemented in the same function.
However,
there is a major drawback to using these functions: your program, when restored
to its previously saved state, will lose its references to any dynamically allocated
memory between the
longjmp() and the
setjmp(). This means you will waste memory for every malloc() or calloc() you
have implemented between your longjmp() and setjmp(), and your program will be
horribly inefficient. It is highly recommended that you avoid using functions
such
as longjmp() and setjmp() because they,
like the goto statement, are quite often an indication of poor programming
practice.
100.How is a file
closed ?
Ans:
A
file is closed using fclose() function Eg. fclose(fp);
Where fp is a file
pointer.
101.What
is a random access file? Ans:
A file can be
accessed at random using fseek() function fseek(fp,position,origin);
fp
file pointer position number of bytes offset from origin origin 0,1 or 2 denote
the beginning ,current position or end of file respectively.
102.What is the
purpose of ftell ?
Ans:
The
function ftell() is used to get the current file represented by the file
pointer. ftell(fp);
returns
a long integer value representing the current file position of the file pointed
by the file pointer fp.If an error occurs ,-1 is returned.
103.What is the
purpose of rewind() ?
Ans:
The
function rewind is used to bring the file pointer to the beginning of the file.
Rewind(fp);
Where
fp is a file pointer.Also we can get the same effect by feek(fp,0,0);
104.Is the allocated
space within a function automatically deallocated when the function returns?
Ans:
No
pointer is different from what it points to .Local variables including local
pointers
variables
in a function are deallocated automatically when function returns.,But in case
of a
local pointer
variable ,deallocation means that the pointer is deallocated and not the block
of
memory
allocated to it. Memory dynamically allocated always persists until the
allocation is freed or the program terminates.
105.Discuss
on pointer arithmetic? Ans:
1-
Assignment of pointers to the same type of pointers. 2- Adding or subtracting a
pointer and an integer. 3-subtracting or comparing two pointer.
4-incrementing
or decrementing the pointers pointing to the elements of an array. When a
pointer
to an integer is
incremented by one , the address is incremented by two. It is done
automatically
by the compiler.
5-Assigning the value
0 to the pointer variable and comparing 0 with the pointer. The pointer
having address 0
points to nowhere at all.
106.What
is the invalid pointer arithmetic? Ans:
i) adding ,multiplying
and dividing two pointers.
ii) Shifting or masking
pointer.
iii) Addition of float or
double to pointer.
iv) Assignment of a
pointer of one type to a pointer of another type
107.What are the
advantages of using array of pointers to string instead of an array of strings?
Ans:
i) Efficient use of
memory.
ii) Easier to exchange
the strings by moving their pointers while sorting.
108.What
is the difference between text and binary modes?
Ans:
Streams can be classified into two types: text streams and
binary streams. Text streams are
interpreted, with a maximum length of 255 characters. With text streams,
carriage return/line feed combinations are translated to the newline n
character and vice versa. Binary streams are uninterrupted and are treated one
byte at a time with no translation of characters. Typically, a text stream
would be used for reading and writing standard text files, printing output to
the screen or
printer, or receiving input from the keyboard. A binary text
stream would typically be used for reading and writing binary files such as
graphics or word processing documents, reading mouse input, or reading and
writing to the modem.
109.Are the
expressions *ptr ++ and ++ *ptr same?
Ans:
No,*ptr
++ increments pointer and not the value pointed by it. Whereas ++ *ptr increments
the value being pointed to by ptr.
110.What
would be the equivalent pointer expression foe referring the same element as
a[p][q][r][s] ?
Ans : *( * ( * ( * (a+p) +
q ) + r ) + s)
111.Are
the variables argc and argv are always local to main? Ans: Yes
they are local to main.
112.Can main () be
called recursively?
Ans: Yes any function
including main () can be called recursively.
