C Files Program - How the data stored on the disk is read

   #include <stdio.h>
   #include <stdlib.h>
   void main()
   {
     FILE *fptr;
     char filename[15];
     char ch;
     printf("Enter the filename to be opened\n");
     gets(filename);
     fptr = fopen (filename, "r"); /*open for reading*/
     if (fptr == NULL)
     {
       printf("Cannot open file\n");
       exit(0);
     }
     ch = fgetc(fptr);
     while (ch != EOF)
     {
       printf ("%c", ch);
       ch = fgetc(fptr);
     }
     fclose(fptr);
   }