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Example programs showing pointer assignment, addition and subtractions in Data Structures through 'C'

Example programs showing pointer assignment, addition and subtractions:


1.’C’ program to read and print a dynamic array of the user required size:
   #include<stdio.h>
  #include<conio.h>
  #include<stdlib.h>
main(),
{
 int *arr, size, i;
 /* arr is a pointer to store address of dynamically allocated memory*/
 clrscr();
 printf(“Enter the size of array :”);
 scanf(“%d”,&size);
  arr=(int*)malloc(size*sizeof(int));
   /* dynamic memory allocation, pointer assignment operation */

  If(arr= = NULL)
 {
   printf(“Memory allocation error!”);
   exit(0);        /*to terminate program execution */
 }    /*end of if*/
 printf(“\n Enter array elements:”);
 for(i=0;i<size;i++)
    scanf(“%d”,arr+i);                                 /*pointer
addition */
  printf(“\nThe array is:\n”);
  for(i=0;i<size;i++)
  printf(“%d”,*(arr+i));                                  /*pointer
 addition */

}             /* end of main() */


NOTE: The array elements can also be referred as arr[i],
Where ’i’ is the index of the respective element.
The same program 1 for reading and displaying dynamic array can also be written with pointer subtraction as follows:

To read the array and display the array using pointer subtraction operation, the address of the last element is stored in a pointer variable and it is update accordingly by subtracting the respective index of the element to be read or displayed.
   #include<stdio.h>
  #include<conio.h>
  #include<stdlib.h>
main(),
{
  int *arr, size, i,*p;
  /* arr is a pointer to store address of dynamically allocated memory*/
  clrscr();
  printf(“Enter the size of array :”);
  scanf(“%d”,&size);

   arr=(int*)malloc(size*sizeof(int));
   /* dynamic memory allocation, pointer assignment operation */

   if(arr= = NULL)
   {
     printf(“Memory allocation error!”);
     exit(0);        /*to terminate program execution */
     }    /*end of if*/

  p=&a[size-1];/*address of the last element */
  printf(“\n Enter array elements:”);
  for(i=size-1;i>=0;i--)
   scanf(“%d”,p-i);                   /*pointer subtraction*/

  p=&a[size-1]; /*pointer assignment */
  printf(“\nThe array is:\n”);
  for(i=0;i<size;i++)
   printf(“%d”,*(p-i));      /*pointer subtraction*/

}             /* end of main() */

2.’C’ program to implement to searching using dynamic array:


   #include<stdio.h>
  #include<conio.h>
  #include<stdlib.h>
main(),
{
 float *arr, num;  /*array of real numbers */
 int size, i;
 clrscr();
 printf(“Enter the size of array :”);
 scanf(“%d”,&size);
 arr=(float*)malloc(size*sizeof(float));
 if(arr = = NULL)
 {
  printf(Memory allocation error!);
  exit(0);    /*to terminate program execution */
 }        /* end of it*/
 printf(“\nEnter  array elements:”);
 for(i=0;i<size;i++)
 scanf(“%f”,arr+i);                                      /*pointer addition */
 printf(“Enter the real number to search in array:”);
 scanf(“%f”,&num);
 for(i=0;i<size;i++)
   if(num==*(arr+i))
   break;                /*to terminate for loop */
 if(i==size)            /*if i=size then ‘break’ is not executed.
                               Element comparison is over */
 printf(“Search unsuccessful…”);
 else
 printf(“Search successful…”);
} /*end of main() */

3.’C’ program to count the frequency of a number in a dynamic array.

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
main(),
{
  float *arr, num;  /*array of real numbers */
  int size, i, count=0;
  printf(“Enter the size of array :”);
  scanf(“%d”,&size);
  arr=(float*)malloc(size*sizeof(float));
  if(arr == NULL)
 {
   printf(Memory allocation error!);
   exit(0);    /*to terminate program execution */
 }        /* end of it*/
  printf(“\nEnter  array elements:”);
  for(i=0;i<size;i++)
  scanf(“%f”,arr+i);                                      /*pointer addition */
  printf(“Enter the number, the freq. of which is freq.:”);
  scanf(“%f”,&num);
   /*finding the frequency */
  for(i=0;i<size;i++)
   if(num==*(arr=i))
     count++;        /*count incremented by 1, whenever the num is equal to
                              the array element */                                
  printf(“\n Frequency of number %f is %d”,num,count);
} /*end of main() */

4.’C’ program to find the number of prime numbers stored in a dynamic array.

  #include<stdio.h>
 #include<conio.h>
 #include<stdlib.h>
 int prime(int num)
{
  int i;
  for(i=2;i<=num/2;i++)
  if(num%i == 0)               /*Non-prime */
     return 0;
  return 1;               /*prime */
 }
main()
{
  int  *arr, size, i, count=0;

  printf(“Enter the size of array :”);
  scanf(“%d”,&size);

  arr=(int*)malloc(size*sizeof(int));
  if(arr == NULL)
 {
   printf(“Memory allocation error!”);
   exit(0);                                /*to terminate program execution */
}                         /* end of it*/
 printf(“\nEnter  array elements:”);
 for(i=0;I<size;i++)
 scanf(“%d”,arr+i);                                      /*pointer addition */
 for(i=0;i<size;i++)
 if(prime(*(arr+i)) ==1)
 count++;                                    
 printf(“\nNumber of primes = %d”,count);
} /*end of main() *

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