/* Random access with fseek(). */
#include <stdlib.h>
#include <stdio.h>
#include <io.h>

#define MAX 50

main()
{
     FILE *fp;
     int data, count, array[MAX];
     long offset;

     /* Initialize the array. */

     for (count = 0; count < MAX; count++)
         array[count] = count * 10;

     /* Open a binary file for writing. */

     if ( (fp = fopen("RANDOM.DAT", "wb")) == NULL)
     {
         fprintf(stderr, "\nError opening file.");
         exit(1);
     }

     /* Write the array to the file, then close it. */

     if ( (fwrite(array, sizeof(int), MAX, fp)) != MAX)
     {
         fprintf(stderr, "\nError writing data to file.");
         exit(1);
     }

     fclose(fp);

     /* Open the file for reading. */

     if ( (fp = fopen("RANDOM.DAT", "rb")) == NULL)
     {
         fprintf(stderr, "\nError opening file.");
         exit(1);
     }

     /* Ask user which element to read. Input the element */
     /* and display it, quitting when -1 is entered. */

     while (1)
     {
         printf("\nEnter element to read, 0-%d, -1 to quit: ",MAX-1);
         scanf("%ld", &offset);

         if (offset < 0)
             break;
         else if (offset > MAX-1)
             continue;

         /* Move the position indicator to the specified element. */

         if ( (fseek(fp, (offset*sizeof(int)), SEEK_SET)) != 0)
         {
             fprintf(stderr, "\nError using fseek().");
             exit(1);
         }

         /* Read in a single integer. */

         fread(&data, sizeof(int), 1, fp);

         printf("\nElement %ld has value %d.", offset, data);
     }

     fclose(fp);
     return(0);
}