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  c interview6 11/22/2017 3:30am (UTC)
   
 

 

C Interview Questions and Answers-PAGE-6
What are the different storage classes in C?

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 the static specifier also have static scope.

Memory obtained from calls to malloc(), alloc() or realloc() belongs to allocated storage class.



What is the difference between strings and character arrays?

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.



Write down the equivalent pointer expression for referring the same element a[i][j][k][l]?

a[i] == *(a+i)
a[i][j] == *(*(a+i)+j)
a[i][j][k] == *(*(*(a+i)+j)+k)
a[i][j][k][l] == *(*(*(*(a+i)+j)+k)+l)



Which bit wise operator is suitable for checking whether a particular bit is on or off?

The bitwise AND operator. Here is an example:

enum {
KBit0 = 1,
KBit1,

KBit31,
};

if ( some_int & KBit24 )
printf ( “Bit number 24 is ONn” );
else
printf ( “Bit number 24 is OFFn” );



Which bit wise operator is suitable for turning off a particular bit in a number?

The bitwise AND operator, again. In the following code snippet, the bit number 24 is reset to zero.
some_int = some_int & ~KBit24;



Which bit wise operator is suitable for putting on a particular bit in a number?

The bitwise OR operator. In the following code snippet, the bit number 24 is turned ON:
some_int = some_int | KBit24;



Does there exist any other function which can be used to convert an integer or a float to a string?

Some implementations provide a nonstandard function called itoa(), which converts an integer to string.

#include

char *itoa(int value, char *string, int radix);

DESCRIPTION
The itoa() function constructs a string representation of an integer.

PARAMETERS
value:
Is the integer to be converted to string representation.

string:
Points to the buffer that is to hold resulting string.
The resulting string may be as long as seventeen bytes.

radix:
Is the base of the number; must be in the range 2 - 36.

A portable solution exists. One can use sprintf():

char s[SOME_CONST];
int i = 10;
float f = 10.20;

sprintf ( s, “%d %fn”, i, f );

WHat will be the result of the following code? #define TRUE 0 // some code while(TRUE) { // some code }

Answer: This will not go into the loop as TRUE is defined as 0.




What will be printed as the result
of the operation below:

int x;
int modifyvalue()
{
return(x+=10);
}

int changevalue(int x)
{
return(x+=1);
}

void main()
{
int x=10;
x++;
changevalue(x);
x++;
modifyvalue();
printf("First output:%dn",x);

x++;
changevalue(x);
printf("Second output:%dn",x);
modifyvalue();
printf("Third output:%dn",x);

}


Answer: 12 , 13 , 13



What will be printed as the result of the operation below:
main()
{
int x=10, y=15;
x = x++;
y = ++y;
printf(“%d %dn”,x,y);

}


Answer: 11, 16



What will be printed as the result of the operation below:
main()
{
int a=0;
if(a==0)
printf(“Cisco Systemsn”);
printf(“Cisco Systemsn”);

}


Answer: Two lines with “Cisco Systems” will be printed.



What will the following piece of code do
int f(unsigned int x)
{
int i;
for (i=0; x!0; x>>=1){
if (x & 0X1)
i++;
}
return i;
}


Answer: returns the number of ones in the input parameter X



What will happen in these three cases?

if(a=0){
//somecode
}
if (a==0){
//do something
}
if (a===0){
//do something
}



What are x, y, y, u
#define Atype int*
typedef int *p;
p x, z;
Atype y, u;


Answer: x and z are pointers to int. y is a pointer to int but u is just an integer variable



What does static variable mean?

there are 3 main uses for the static.
1. If you declare within a function:
It retains the value between function calls

2.If it is declared for a function name:
By default function is extern..so it will be visible from other files if the function declaration is as static..it is invisible for the outer files

3. Static for global variables:
By default we can use the global variables from outside files If it is static global..that variable is limitied to with in the file



Advantages of a macro over a function?

Macro gets to see the Compilation environment, so it can expand __ __TIME__ __FILE__ #defines. It is expanded by the preprocessor.

For example, you can’t do this without macros
#define PRINT(EXPR) printf( #EXPR “=%dn”, EXPR)

PRINT( 5+6*7 ) // expands into printf(”5+6*7=%d”, 5+6*7 );

You can define your mini language with macros:
#define strequal(A,B) (!strcmp(A,B))

Macros are a necessary evils of life. The purists don’t like them, but without it no real work gets done.



What are the differences between malloc() and calloc()?

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() doesnot initialize the memory allocated, while calloc() initializes the allocated memory to ZERO.

What will print out?
main()
{
char *p1=“name”;
char *p2;
p2=(char*)malloc(20);
memset (p2, 0, 20);
while(*p2++ = *p1++);
printf(“%sn”,p2);
}

The pointer p2 value is also increasing with p1 .
*p2++ = *p1++ means copy value of *p1 to *p2 , then increment both addresses (p1,p2) by one , so that they can point to next address . So when the loop exits (ie when address p1 reaches next character to “name” ie null) p2 address also points to next location to “name” . When we try to print string with p2 as starting address , it will try to print string from location after “name” … hense it is null string ….

eg :
initially p1 = 2000 (address) , p2 = 3000
*p1 has value “n” ..after 4 increments , loop exits … at that time p1 value will be 2004 , p2 =3004 … the actual result is stored in 3000 - n , 3001 - a , 3002 - m , 3003 -e … we r trying to print from 3004 …. where no data is present … thats why its printing null .

Answer:empty string.



What will be printed as the result of the operation below:
main()
{
int x=20,y=35;
x=y++ + x++;
y= ++y + ++x;
printf(“%d%dn”,x,y)
;
}


Answer : 5794



What will be printed as the result of the operation below:
main()
{
int x=5;
printf(“%d,%d,%dn”,x,x<<2,>>2)
;
}


Answer: 5,20,1



What will be printed as the result of the operation below:
#define swap(a,b) a=a+b;b=a-b;a=a-b;
void main()
{
int x=5, y=10;
swap (x,y);
printf(“%d %dn”,x,y)
; swap2(x,y);
printf(“%d %dn”,x,y)
; }

int swap2(int a, int b)
{
int temp;
temp=a;
b=a;
a=temp;
return 0;
}


as x = 5 = 0×0000,0101; so x << 2 -< 0×0001,0100 = 20; x >7gt; 2 -> 0×0000,0001 = 1. Therefore, the answer is 5, 20 , 1

the correct answer is
10, 5
5, 10


Answer: 10, 5



What will be printed as the result of the operation below:
main()
{
char *ptr = ” Cisco Systems”;
*ptr++; printf(“%sn”,ptr)
; ptr++;
printf(“%sn”,ptr);

}


1) ptr++ increments the ptr address to point to the next address. In the prev example, ptr was pointing to the space in the string before C, now it will point to C.

2)*ptr++ gets the value at ptr++, the ptr is indirectly forwarded by one in this case.

3)(*ptr)++ actually increments the value in the ptr location. If *ptr contains a space, then (*ptr)++ will now contain an exclamation mark.

Answer:Cisco Systems



What will be printed as the result of the operation below:
main()
{
char s1[]=“Cisco”;
char s2[]= “systems”;
printf(“%s”,s1)
; }


Answer: Cisco



What will be printed as the result of the operation below:
main()
{
char *p1;
char *p2;

p1=(char *)malloc(25);
p2=(char *)malloc(25);

strcpy(p1,”Cisco”);
strcpy(p2,“systems”);
strcat(p1,p2);

printf(“%s”,p1)
;
}


Answer: Ciscosystems



The following variable is available in file1.c, who can access it?: static int average;

Answer: all the functions in the file1.c can access the variable.
 
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