Illustration of error handling in file operation

Program 63) Write a program to illustrate error handlingin file operations.

This program shows illustrates the use of the NULL pointer test and feof function. When we input filename as TETS, the function call
                            fopen ("TETS", "r") ;
returns a NULL pointer because the file TETS does not exist and therefore the message "Cannot open the file" is printed out.
Similarly, the call, foef(fp2) returns a nonzero integer when the entire data has been read, and hence the program prints the message "Ran out of data" and terminates further reading.

                                 PROGRAM

#include <stdio.h>
main ( )
 {
         char *filename ;
          FILE   *fp1, *fp2 ;
          int i, number ;

        fp1 = fopen ("TESTA", "w") ;
        for (i = 10; i <= 100; i += 10)
                  putw (i, fp1) ;

        fclose (fp1) ;

       printf ("\nInput filename\n") ;

 open_file:
       scanf ("%s", filename) ;

      if ((fp2 = fopen (filename, "r")) == NULL)
      {
          printf ("Cannot open the file.\n") ;
          printf ("Type filename again.\n\n") ;
          goto open_file ;
      }
     else
     for (i = 1; i <= 20; i++)
     {    number = getw(fp2) ;
          if (feof (fp2))
          {
               printf ("\nRan out of data.\n") ;
               break ;
          }
          else
               printf ("%d\n", number) ;
     }
     fclose (fp2) ;
 }

Output:           Input filename
                       TETS
                       Cannot open the file
                       Type filename again

                       TEST
                        10
                        20
                        30
                        40
                        50 
                        60
                        70 
                        80
                        90
                       100

        Ran out of data