Difference between revisions of "Interview Preparation topic : Pointers in C"

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<b>Interview Questions on pointers : </b>
 
<b>Interview Questions on pointers : </b>
  
1) What is a NULL Pointer?<br>
+
1) What is a NULL pointer?<br>
->A pointer pointing to nothing is called as a NULL Pointer Eg: int *x=NULL;<br>
+
-> A pointer pointing to nothing is called as a NULL Pointer Eg: int *x=NULL;<br>
  
2)
+
2) What is a dangling pointer><br>
 +
-> Dangling Pointer is a pointer that doesn’t point to a valid memory location. Initially the pointer holds a valid address but later the held address is released or freed.
 +
 
 +
3) What is a void pointer?<br>.
 +
->In C General Purpose Pointer is called as void Pointer. It does not have any data type associated with it and can store address of any type of variable
 +
  for eg void *ptr;    // ptr is declared as Void pointer
 +
      char cnum;
 +
      int inum;
 +
      float fnum;
 +
      ptr = &cnum;  // ptr has address of character data
 +
      ptr = &inum;  // ptr has address of integer data
 +
      ptr = &fnum;  // ptr has address of float data
 +
 
 +
4) What is the difference between *ptr++ and ++*ptr?

Revision as of 23:59, 10 December 2016

What is a Pointer?

A pointer is a variable which contains the address in memory of another variable. Every variable is a memory location and every memory location has its address defined which can be accessed using ampersand (&) operator, which denotes an address in memory.

Lets Look at the following example:

  1. include <stdio.h>

int main ()

{
  int  temp;
  int temp1;
  printf("Address of temp variable: %x\n", &temp );
  printf("Address of temp1 variable: %x\n", &temp1 );
  return 0;

}

When the following code is compiled and executed:
Address of temp variable: edf53400
Address of temp1 variable: adf9a5f6


To declare a pointer to a variable do:

type *pointer;

Where type can be int, double, float, char and pointer can be any variable.


Consider the following example:

  1. include <stdio.h>

int main () {

  int  temp= 100;                                     /* Stores the value 20 in variable temp */
  int  *ptr;                                          /* Declares a pointer variable of type int */
  ip = &temp;                                         /*store address of temp in pointer variable, so now the address of temp will be in ptr */
  printf("Address of temp variable: %x\n", &temp);    /* print the address of variable temp */
  printf("Address stored in ptr variable: %x\n",ptr ); /* prints the address stored in variable ptr */
  printf("Value of *ptr variable: %d\n", *ptr );       /* prints the value stored at address ptr, this is also known as dereferencing of a pointer */
  return 0;

}

When we compile and execute the following code:
Address of temp variable: a54fae34
Address stored in ptr variable: a54fae34
Value of *ptr variable:100


Interview Questions on pointers :

1) What is a NULL pointer?
-> A pointer pointing to nothing is called as a NULL Pointer Eg: int *x=NULL;

2) What is a dangling pointer>
-> Dangling Pointer is a pointer that doesn’t point to a valid memory location. Initially the pointer holds a valid address but later the held address is released or freed.

3) What is a void pointer?
. ->In C General Purpose Pointer is called as void Pointer. It does not have any data type associated with it and can store address of any type of variable

 for eg void *ptr;    // ptr is declared as Void pointer
     char cnum;
     int inum;
     float fnum;
     ptr = &cnum;  // ptr has address of character data
     ptr = &inum;  // ptr has address of integer data
     ptr = &fnum;  // ptr has address of float data

4) What is the difference between *ptr++ and ++*ptr?