Difference between revisions of "Interview Preparation Pointers"

Revision as of 17:40, 18 December 2016

Pointers : A pointer is a variable who's value is address of some other variable i.e. it can be address of some memory location.

<varaible_type> *<name>
eg : 
     int *pointer_to_integer

The above example , we have declared a pointer to a variable (pointer_to_integer), the variable stores the address of an integer .

Implementation of Pointer :

Code:

#include <stdio.h>
int main(void) {
	int var = 20;
	int *p;
	p = &var;
	
	printf("Pointer %d\n",var);
	printf("Pointer %d\n",&var);     // Prints the address of the varaible (var)
	printf("Pointer %d\n",p);        
	printf("Pointer %d\n",*p);	     // Prints the value that (p) points to   
	return 0;
}

Output :

Pointer 20
Pointer 1809844068
Pointer 1809844068
Pointer 20

Malloc

  The Malloc function dynamically allocates memory when required. The function allocates size of byte of memory and returns a pointer to the first byte of NULL.

Syntax:
pointer = (type)malloc(size in bytes);
 
Code:

int* p;                        //Declare pointer                          
p = (int*)malloc(sizeof(int)); // Pointer equal to pointer type int that contain memory address space of int
*p = 5;                        // Finally pointer points to location containing value 5

Passing Pointers to a Function

  In the code below we have a defines a function values , which return void . It takes two parameters which are pointers to an integer. When the function is called the address of the integer is passed and not the value .    
  

Code:

#include <stdio.h>
 
/* function declaration */
void value(int *num_ptr_1, int *num_ptr_2);
 
int main () {

   /* local variable definition */
   int a = 100;
   int b = 200;
 
   /* calling a function value */
      value(&a, &b);
 
   return 0;
}
 
/* function prints the value of  two numbers */
void value(int *num1, int *num2) {
    
 printf("The value of num1 is %d & num2 is %d", *num1 , *num2 );
    
}

Output :

The value of num1 is 100 & num2 is 200

Passing Pointer from a function

Code:
#include <stdio.h>

 
/* function  return max number. */
int* getMax( ) {

   static int  a = 100;
   static int  b = 200;
 
    if (a > b)
    {
       return &a;        
    }
    else
    {
        return &b;
    }
}
 
/* main function to call above defined function */
int main () {

   /* a pointer to an int */
   int *p;

   p = getMax();
   printf("The Max value is  %d\n", *p);

   return 0;
}

Output :

The Max value is 200