Q:What will be the output of the following code?
void main ()
{
int i = 0 , a[3] ;
a[i] = i++;
printf (“%d",a[i]) ;
}
Ans: The output for the above code would be a
garbage value. In the statement a[i] = i++; the value of the variable i
would get assigned first to a[i] i.e. a[0] and then the value of i
would get incremented by 1. Since a[i] i.e. a[1] has not been initialized, a[i]
will have a garbage value.
Q:Why doesn't the following code give the desired result?
A: int x = 3000, y = 2000 ;
long int z = x * y ;
Ans: Here
the multiplication is carried out between two ints x and y, and the
result that would overflow would be truncated before being assigned to
the variable z of type long int. However, to get the correct output,
we should use an explicit cast to force long arithmetic as shown below:
long int z = ( long int ) x * y ;
Note that ( long int )( x * y ) would not give the desired effect.
Q: Why doesn't the following statement work?
A:
char str[ ] = "Hello" ;
strcat ( str, '!' ) ;
Ans: The string function strcat( ) concatenates
strings and not a character. The basic difference between a string and a
character is that a string is a collection of characters, represented by an
array of characters whereas a character is a single character. To make the
above statement work writes the statement as shown below:
strcat ( str, "!" ) ;
Q:How do I know how many elements an array can hold?
A: The amount of
memory an array can consume depends on the data type of an array. In
DOS
environment, the amount of memory an array can consume depends on the current
memory model (i.e. Tiny, Small, Large, Huge, etc.). In general an array cannot
consume more than 64 kb. Consider following program, which shows the maximum
number of elements an array of type int, float and char can have in case of
Small memory model.
main( )
{
int i[32767] ;
float f[16383] ;
char s[65535] ;
}
Q:How do I write code that reads data at memory location
specified by segment and offset?
A: Use peekb( )
function. This function returns byte(s) read from specific segment and offset
locations in memory. The following program illustrates use of this function. In
this program from VDU memory we have read characters and its attributes of the
first row. The information stored in file is then further read and displayed
using peek( ) function.
#include
#include
main( )
{
char far *scr = 0xB8000000 ;
FILE *fp ;
int offset ;
char ch ;
if ( ( fp = fopen ( "scr.dat", "wb" ) ) ==
NULL )
{
printf ( "\nUnable to open file" ) ;
exit( ) ;
}
// reads and writes to file
for ( offset = 0 ; offset < 160 ; offset++ )
fprintf ( fp, "%c", peekb ( scr, offset ) ) ;
fclose ( fp ) ;
if ( ( fp = fopen ( "scr.dat", "rb" ) ) ==
NULL )
{
printf ( "\nUnable to open file" ) ;
exit( ) ;
}
// reads and writes to file
for ( offset = 0 ; offset < 160 ; offset++ )
{
fscanf ( fp, "%c", &ch ) ;
printf ( "%c", ch ) ;
}
fclose ( fp ) ;
}
Q: What is C language?
A: 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.
Q: Inprintf() Function What is the output of
printf("%d")?
A:1. When we write
printf("%d",x); this means compiler will print the value of x. But as
here, there is nothing after �%d� so compiler will show in output window
garbage value.
2. When we use %d the compiler internally uses it to access
theargument in the stack (argument stack). Ideally compiler determines
the offset of the data variable depending on the
format specification string. Now when we write printf("%d",a)
then compiler first accesses the top most element in
the argument stack of the printf which is %d and depending
on the format string it calculated to offset to the actual
datavariable in the memory which is to be printed. Now when only %d will
be present in the printf then compiler will calculate the correct
offset (which will be the offset to access the integer variable) but as
the actual data object is to be printed is not present at that memory location
so it will print what ever will be the contents of that memory location.
3. Some compilers check the format string and
will generate an error without the proper number and type of arguments for
things like printf(...) and scanf(...).
Q:malloc() Function- What is the difference between
"calloc(...)" and "malloc(...)"?
A: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.
Q: In printf() Function- What is the difference between
"printf(...)" and "sprintf(...)"?
A: sprintf(...) writes data to the character array
whereas printf(...) writes data to the standard output device.
Q:Compilation How to reduce a final size of executable?
A:Size of the final
executable can be reduced using dynamic linking for libraries.
Q:Linked Lists -- Can you tell me how to check
whether a linked list is circular?
A:Create two pointers, and set both to the
start of the list. Update each as follows:
|
|
while (pointer1) {
pointer1 = pointer1->next;
pointer2 = pointer2->next;
if (pointer2) pointer2=pointer2->next;
if (pointer1 == pointer2) {
print ("circular");
}
}
If a list is circular, at some point pointer2 will wrap around
and be either at the item just before pointer1, or the item before that. Either
way, its either 1 or 2 jumps until they meet.
Q:string Processing --- Write out a function that prints out all
the permutations of a string. For example, abc would give you abc, acb, bac,
bca, cab, cba.
A:void PrintPermu (char
*sBegin, char* sRest) {
int iLoop;
char cTmp;
char cFLetter[1];
char *sNewBegin;
char *sCur;
int iLen;
static int iCount;
iLen = strlen(sRest);
if (iLen == 2) {
iCount++;
printf("%d: %s%s\n",iCount,sBegin,sRest);
iCount++;
printf("%d:
%s%c%c\n",iCount,sBegin,sRest[1],sRest[0]);
return;
} else if (iLen == 1) {
iCount++;
printf("%d: %s%s\n", iCount, sBegin, sRest);
return;
} else {
// swap the first character of sRest with each of
// the remaining chars recursively call debug print
sCur = (char*)malloc(iLen);
sNewBegin = (char*)malloc(iLen);
for (iLoop = 0; iLoop <>
strcpy(sCur, sRest);
strcpy(sNewBegin, sBegin);
cTmp = sCur[iLoop];
sCur[iLoop] = sCur[0];
sCur[0] = cTmp;
sprintf(cFLetter, "%c", sCur[0]);
strcat(sNewBegin, cFLetter);
debugprint(sNewBegin, sCur+1);
}
}
}
void main() {
char s[255];
char sIn[255];
printf("\nEnter a string:");
scanf("%s%*c",sIn);
memset(s,0,255);
PrintPermu(s, sIn);
}
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