#include <stdio.h>
#include <string.h>

#define MAXFILENAMELEN 40
#define MAXLEN 60

void convert( char *file_name );

void main( int argc, char **argv )
{
   char filename [MAXFILENAMELEN];

     if( argc != 2 )
        {
        printf( "\n\nFilename to convert to lower case? " );
        gets( filename );
        }
     else
        strcpy( filename, *( argv + 1 ) );

     convert( filename ); 
}

void convert( char *fname )
{
   char word [MAXLEN];
     
   FILE *fps,
        *fpt;

      fps = fopen( fname, "r" );
      fpt = fopen( "tfile", "w" );

      while( !feof( fps ) )
         {
         fgets( word, MAXLEN - 1, fps );

         if( feof( fps ) ) break;

         strlwr( word );
         fputs( word, fpt );

         }

      fclose( fps );
      fclose (fpt );

      unlink( fname );
      rename( "tfile", fname );
     
      return;
}