C Prog Interview q Ptr

C programming interview questions and answersC interview questions and answer for freshers or beginners, placement questions papers, code examples on c++ tutorial

C POINTER QUESTIONS

C pointers interview questions and answersIt is frequently asked technical objective types multiple choice questions of placement in c programming languageNote: Linux GCC compilers and Visual C++ compiler doesn't support far and huge pointers.

1.What will be output of following program?

#include<stdio.h>int main(){ int a = 320; char *ptr; ptr =( char *)&a; printf("%d ",*ptr); return 0;}

(A) 2

(B) 320

(C) 64

(D) Compilation error

(E) None of above

E x p l a n a t i o n :

Search

Output

Turbo C++ 3.0: 64

Turbo C ++4.5: 64

Linux GCC: 64

Visual C++: 64

As we know int is two byte data byte while char is one byte data byte. char pointer can keep the address one byte at time.

Binary value of 320 is 00000001 01000000 (In 16 bit)

Memory representation of int a = 320 is:

So ptr is pointing only first 8 bit which color is green and Decimal value is 64.


#include<stdio.h>#include<conio.h>int main(){ void (*p)(); int (*q)(); int (*r)(); p = clrscr; q = getch; r = puts;

http://4.bp.blogspot.com/_uIwyaTjqYYw/S1IvP59A7nI/AAAAAAAABL0/qy7B9wsrlgk/s1600-h/pointer1.png

(*p)(); (*r)("cquestionbank.blogspot.com"); (*q)(); return 0;}

(A) NULL

(B) cquestionbank.blogspot.com

(C) c


(E) None of above


Turbo C++ 3.0: cquestionbank.blogspot.com

Turbo C ++4.5: cquestionbank.blogspot.com

Linux GCC: Compilation error

Visual C++: Compilation error

p is pointer to function whose parameter is void and return type is also void. r and q is pointer to function whose parameter is void and return type is int . So they can hold the address of such function.


#include<stdio.h>int main(){ int i = 3; int *j; int **k; j=&i; k=&j;

Output

printf("%u %u %d ",k,*k,**k); return 0;}

(A) Address, Address, 3

(B) Address, 3, 3

(C) 3, 3, 3


(E) None of above

Explanation:

Turbo C++ 3.0: Address, Address, 3

Turbo C ++4.5: Address, Address, Address

Linux GCC: Address, Address, 3

Visual C++: Address, Address, 3

Memory representation

Here 6024, 8085, 9091 is any arbitrary address, it may be different.

Value of k is content of k in memory which is 8085

Value of *k means content of memory location which address k keeps.

Output

http://1.bp.blogspot.com/_uIwyaTjqYYw/S1IvRjLO-bI/AAAAAAAABL8/yAFJiZiIekk/s1600-h/pointer2.png

k keeps address 8085 .

Content of at memory location 8085 is 6024

In the same way **k will equal to 3.

Short cut way to calculate:

Rule: * and & always cancel to each otheri.e. *&a = aSo *k = *(&j) since k = &j*&j = j = 6024And**k = **(&j) = *(*&j) = *j = *(&i) = *&i = i = 3


#include<stdio.h>int main(){ char far *p =(char far *)0x55550005; char far *q =(char far *)0x53332225; *p = 80; (*p)++; printf("%d",*q); return 0;}

(A) 80

(B) 81

(C) 82


(E) None of above


Turbo C++ 3.0: 81

Turbo C ++4.5: Compilation error

Output



Far address of p and q are representing same physical address.

Physical address of 0x55550005 = (0x5555) * (0x10) + (0x0005) = 0x55555

Physical address of 0x53332225 = (0x5333 * 0x10) + (0x2225) = 0x55555

*p = 80, means content at memory location 0x55555 is assigning value 25

(*p)++ means increase the content by one at memory location 0x5555 so now content at memory location 0x55555 is 81

*q also means content at memory location 0x55555 which is 26


#include<stdio.h>#include<string.h>int main(){

char *ptr1 = NULL;char *ptr2 = 0;strcpy(ptr1," c");strcpy(ptr2,"questions");printf("\n%s %s",ptr1,ptr2);return 0;

}

(A) c questions

(B) c (null)

(C) (null) (null)


(E) None of above


Turbo C++ 3.0: (null) (null)

Turbo C ++4.5: Run time error

Linux GCC: Run time error

Visual C++: Run time error

We cannot assign any string constant in null pointer by strcpy function.


#include<stdio.h>int main(){

int huge *a =(int huge *)0x59990005;int huge *b =(int huge *)0x59980015;if(a == b)printf("power of pointer");elseprintf("power of c");return 0;

}

(A) power of pointer

(B) power of c

(C) power of cpower of c


(E) None of above


Output

Output

Turbo C++ 3.0: power of pointer

Turbo C ++4.5: power of c



Here we are performing relational operation between two huge addresses. So first of all both a and b will normalize as:

a= (0x5999)* (0x10) + (0x0005) =0x9990+0x0005=0x9995

b= (0x5998)* (0x10) + (0x0015) =0x9980+0x0015=0x9995

Here both huge addresses are representing same physical address. So a==b is true.



register a = 25;int far *p;p=&a;printf("%d ",*p);return 0;

}

(A) 25

(B) 4

(C) Address


(E) None of above


Output

Turbo C++ 3.0: Compilation error




Register data type stores in CPU. So it has not any memory address. Hence we cannot write &a.



char far *p,*q;printf("%d %d",sizeof(p),sizeof(q));return 0;

}

(A) 2 2

(B) 4 4

(C) 4 2

(D) 2 4

(E) None of above

E x p l a n a t i o n :Turbo C++ 3.0: 4 4

Turbo C ++4.5: 4 4



Output

p is far pointer which size is 4 byte.

By default q is near pointer which size is 2 byte.



int a = 10;void *p = &a;int *ptr = p;printf("%u",*ptr);return 0;

}

(A) 10

(B) Address

(C) 2


(E) None of above


Turbo C++ 3.0: 10

Turbo C ++4.5: 10

Linux GCC: 10

Visual C++: 10

Void pointer can hold address of any data type without type casting. Any pointer can hold void pointer without type casting.


Output


int register a;scanf("%d",&a);printf("%d",a);return 0;

}//if a=25

(A) 25

(B) Address

(C) 0


(E) None of above






Register data type stores in CPU. So it has not any memory address. Hence we cannot write &a.



char arr[10];arr = "world";printf("%s",arr);

Output

return 0;}

(A) world

(B) w

(C) Null


(E) None of above






Compilation error Lvalue required

Array name is constant pointer and we cannot assign any value in constant data type after declaration.



int a,b,c,d;char *p = ( char *)0;int *q = ( int *q)0;float *r = ( float *)0;double *s = 0;a = (int)(p+1);b = (int)(q+1);c = (int)(r+1);

Output

d = (int)(s+1);printf("%d %d %d %d",a,b,c,d);

return 0;}

(A) 2 2 2 2

(B) 1 2 4 8

(C) 1 2 2 4


(E) None of above


Turbo C++ 3.0: 1 2 4 8




Address + 1 = next address

Since initial address of all data type is zero. So its

next address will be size of data type.



int a = 5,b = 10,c;int *p = &a,*q = &b;c = p - q;printf("%d" , c);

Output

return 0;}

(A) 1

(B) 5

(C) -5


(E) None of above


Turbo C++ 3.0: 1

Turbo C ++4.5: 1

Linux GCC: 1

Visual C++: 2

Difference of two same type of pointer is always one.


#include<stdio.h>unsigned long int (* avg())[3]{

static unsigned long int arr[3] = {1,2,3};return &arr;

}int main(){

unsigned long int (*ptr)[3];ptr = avg();printf("%d" , *(*ptr+2));return 0;

}

(A) 1

(B) 2

Output

(C) 3


(E) None of above

E x p l a n a t i o n :Turbo C++ 3.0: 3

Turbo C ++4.5: 3

Linux GCC: 3

Visual C++: 3



int * p , b;b = sizeof(p);printf("%d" , b);

return 0;}

(A) 2

(B) 4

(C) 8


(E) None of above


Turbo C++ 3.0: 2 or 4

Turbo C ++4.5: 2 or 4

Output

Output

Linux GCC: 4

Visual C++: 4

since in this question it has not written p is which type of pointer. So its output will depend upon which memory model has selected. Default memory model is small.



int i = 5 , j;int *p , *q;p = &i;q = &j;j = 5;printf("%d %d",*p,*q);return 0;

}

(A) 5 5

(B) Address Address

(C) 5 Address


(E) None of above


Turbo C++ 3.0: 5 5

Turbo C ++4.5: 5 5

Linux GCC: 5 5

Visual C++: 5 5

Output



int i = 5;int *p;p = &i;printf(" %u %u", *&p , &*p);return 0;

}

(A) 5 Address

(B) Address Address

(C) Address 5


(E) None of above


Turbo C++ 3.0: Address Address

Turbo C ++4.5: Address Address

Linux GCC: Address Address

Visual C++: Address Address

Since * and & always cancel to each other.

i.e. *&a = a

so *&p = p which store address of integer i

&*p = &*(&i) //since p = &i

= &(*&i)

= &i

Output

So second output is also address of i



int i = 100;printf("value of i : %d addresss of i : %u",i,&i);i++;printf("\nvalue of i : %d addresss of i :

%u",i,&i);return 0;

}

(A)value of i : 100 addresss of i : Addressvalue of i : 101 addresss of i : Address(B)value of i : 100 addresss of i : Addressvalue of i : 100 addresss of i : Address(C)value of i : 101 addresss of i : Addressvalue of i : 101 addresss of i : Address(D) Compilation error

(E) None of above


Turbo C++ 3.0:

value of i : 100 addresss of i : Address


Turbo C ++4.5:



Output

Linux GCC:value of i : 100 addresss of i : Addressvalue of i : 101 addresss of i : Address Visual C++:value of i : 100 addresss of i : Addressvalue of i : 101 addresss of i : Address

Within the scope of any variable, value of variable may change but its address will never change in any modification of variable.


#include<stdio.h> int main(){

char far *p =(char far *)0x55550005;char far *q =(char far *)0x53332225;*p = 25;(*p)++;printf("%d",*q);return 0;

}

(A) 25

(B) Address

(C) Garbage


(E)None of above


Turbo C++ 3.0: 26



Output


Far address of p and q are representing same physical address. Physical address of

0x55550005 = 0x5555 * ox10 + ox0005 = 0x55555

Physical address of

0x53332225 = 0x5333 * 0x10 + ox2225 = 0x55555

*p = 25, means content at memory location 0x55555 is assigning value 25

(*p)++ means to increase the content by one at memory the location 0x5555 so now content of memory location at 0x55555 is 26

*q also means content at memory location 0x55555 which is 26


#include<stdio.h> int main(){

int i = 3;int *j;int **k;j = &i;k = &j;printf("%u %u %u",i,j,k);

return 0;}

(A) 3 Address 3

(B) 3 Address Address

(C) 3 3 3


(E) None of above


Turbo C++ 3.0: 3 Address Address

Turbo C ++4.5: 3 Address Address

Linux GCC: 3 Address Address

Visual C++: 3 Address Address

Here 6024, 8085, 9091 is any arbitrary address, it may be different.

Pointer Tutorial More pointer questionsArray questionsString questionsFunction questions

52 comments:

ajitdubey said...How are you calculating the physical address? U have even given the example like "(0x5999)* (0x10) + (0x0005) =0x9990+0x0005=0x9995". But for me it's difficult to understand. What's the formula or what's the logic??? Plz reply me, I'm stucked.

9/30/09 5:17 PM

Output

http://1.bp.blogspot.com/_uIwyaTjqYYw/S1IvRjLO-bI/AAAAAAAABL8/yAFJiZiIekk/s1600-h/pointer2.png

http://www.blogger.com/email-post.g?blogID=959939550345671470&postID=5821035888972107709

http://www.blogger.com/profile/01874537045229956635

manish said...ajit dubey try to understand by following example:

Example:

(q) What will be physical address of address 0X59994444?

Answer:

Huge address: 0X59994444

Offset address: 0x4444

Segment address: 0x5999

Physical address= Segment address * 0X10 + Offset address

=0X5999 * 0X10 +0X4444

=0X59990 + 0X4444

=0X5DDD4

In binary: 0101 1101 1101 1101 0100

Note: Each hexadecimal digit is represented in 4 bit binary number.Note. 0x represents hexadecimal number.

More detail visit following link:http://c-pointer.blogspot.com

10/8/09 5:04 PM

Anonymous said...BOss u r really GEM ,,fantastic wrk...frm [email protected]

3/13/10 2:40 PM

Anonymous said...Thanks! This helped me a lot.

3/14/10 7:14 PM


Anonymous said...good effort...

4/4/10 8:56 PM

Anonymous said...Badhiya Hain

4/8/10 2:41 AM

jagan said...nice questions i need more questions....

4/11/10 7:56 AM

nidhi said...it was really helpful ..thanks a ton to you

4/19/10 2:06 PM

Sukhwinder said...a lot of thanks to u but some answers are not match when i compile the program on my c++ compiler.pls tell me whats happen.

4/30/10 11:28 PM

Anonymous said...great effort dude..

5/28/10 11:45 PM

hasan said...what is far and volatile?

6/1/10 3:46 AM




Abhishek Singh said...In question 15 , can you make specific what do you mean by "which type of pointer"?Whether it is related to a pointer being near or far ?

6/5/10 2:25 AM

Anonymous said...how many types of pointer

6/5/10 12:11 PM

Ranjita Das said...this realy help me

6/5/10 12:15 PM

Arunjunaivelan said...Really gud work

6/17/10 11:08 AM

Anonymous said...Hi

The answer to first question should depend on big or little endian-ness of the machine on which the code is run. On little Endian machine it will give 64 as answer.

6/26/10 5:19 PM

Ritesh kumar said...Hi SukhwinderYes, You are rightAs you know c is not completally platform independent language. Like size of data type, heade file, concept of far,hge pointers etc. varies from compiler to complier. Don't warry. You have to make a little change if you are compiling diffren compilers. Just to inform answer of all questions has checked in turbo c++ 3.0 compiler.

7/8/10 9:43 AM



Ritesh kumar said...Hi Hasan,If you want to know about concept of volatile and far pointer you have to move following link:

Far pointer:http://c-pointer.blogspot.com/2009/06/far-pointer-in-c-programming.html

volatile keyword:http://cbyexample.blogspot.com/2010/02/volatile-keyword-in-c.html

7/8/10 9:49 AM

Ritesh kumar said...Hi Abhishek Singh, exaclty, In question no. 15 meaning of "which type of pointers" indicates near,far and huge pointers.

7/8/10 9:52 AM

Naresh @IITD said...Its very nice....tutorial....Can u please explain multidimensional arrays..

7/31/10 3:20 PM

Anonymous said...Excellent :)

8/19/10 9:52 PM

mayank said...the questions are real good

8/23/10 6:01 PM

Anonymous said...




http://scriptsnest.co.cc/

This is a very good site.. I studied all the questions and concepts and got placed in a good company aswell.. Thanks

9/14/10 12:37 PM

Anonymous said...cool....good1....this is really gonna help many job seekers like me who r preparing for interviews

thanks a lotgod bless !!

9/24/10 1:15 PM

Anonymous said...cool ....absolutely cool

10/18/10 8:15 PM

Anonymous said...Question Number 20:-------------------#include

int main(){int I = 3; // i or I ?int *j;int **k;j = &i;k = &j;printf("%u %u %u",i,j,k);}

/* In the above program i (small letter declared nowhere so obviously it gives compilation errorerror :i was not declared */

I thought you mean to post it to be i instead of I..

The output looks like below :

3 Address Address

If you have a code like this#include

int main()

{int i = 3;int *j;int **k;j = &i;k = &j;printf("%u %u %u",i,j,k);}

rgds,

zapki

12/10/10 11:43 AM

Tewari said...What is lowest valid statment in C ?? and where exactly function pointers are stored in memory ??

1/13/11 4:54 PM

Sara said...Hi , great work...very helpful...i need the explanation for Q 14 .....can u reply me

1/14/11 10:08 PM

checha said...Hi, great work....awesome....very much usefull. need some more questions to bcome perfect in pointers...............

1/18/11 8:49 PM

cristi said...hello, why cannot download this courses?

2/14/11 3:49 AM

Anonymous said...gud workbut try to include C++ also




2/25/11 12:04 AM

Anonymous said...check the last question, its answer is wrong, because variable names are case sensitive

3/2/11 10:04 PM

Anonymous said...Well, I guess some questions are for 16 bit environment. For example, the question 8, I compiled it on Visual Studio 2005 on XP SP3 32bit.The result is 4 4

3/8/11 11:36 PM

Anonymous said...this is the best site for improving c skill.

3/17/11 2:49 PM

Anonymous said...excellent ...............

5/31/11 12:18 PM

Anonymous said...great work...realy good.keep posting newer questions...

6/17/11 6:33 PM

Ravi Gulati said...IN QUES NO. 9,I AM GETTING A COMPILATION ERROR"CAN NOT CONVERT 'VOID *' TO 'INT *'"

CAN U EXPLAIN,Y?

7/9/11 2:23 PM


Vrudijones said...Great collection!

7/16/11 2:04 AM

Anonymous said...Great work dude..:)

9/12/11 9:20 PM

Anonymous said...really good questions

9/27/11 8:00 AM

Anonymous said...good questions and very well described answers . thanks

10/3/11 8:03 PM

BHARAT said...plz tell me leap year condition..............

10/5/11 4:30 AM

BHARAT said...if we divide the year from 4 only .this condition is true or not ? plz tell me

10/5/11 4:32 AM

Ritesh kumar said...Hi Bhart,Go through the following link. http://cquestionbank.blogspot.com/2008/01/write-c-program-for-checking-leap-year.htmlI hope this link will help you.





10/5/11 8:33 AM

game zone said...thanks man......

10/15/11 12:45 AM

lakshmi said...#includeunsigned long int (* avg())[3]{static unsigned long int arr[3] = {1,2,3};return &arr;}int main(){unsigned long int (*ptr)[3];ptr = avg();printf("%d" , *(*ptr+2));return 0;}plz explain why *(*ptr+2) is 3 in this case

10/27/11 11:30 AM

Anonymous said...really these questions helped me alot to understand pointer concepts.thanks alot

11/20/11 12:45 AM

Anonymous said...#includeint main(){char arr[10];arr = "world";printf("%s",arr);return 0;}can aynone of u explain me y d output of tis program is compilation error.please help me.

11/20/11 12:49 AM

Ritesh kumar said...




Hi,char arr[10];In c array name is constant pointer. So it is wrong to write arr = "world";

11/20/11 10:07 AM

Anonymous said...thank u

12/9/11 1:26 PM

Anonymous said...pointer concept i not clear to me .please suggest me any book.

12/16/11 11:19 AM

Anonymous said...this is helpfull for me.........thanks aloat

12/24/11 10:30 PM

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