+ FILE *in, *out;
+ if (argc == 4)
+ {
+ in = fopen(argv[2], "r");
+ if (!in)
+ {
+ fprintf(stderr, "Error opening input file\n");
+ exit(1);
+ }
+ out = fopen(argv[3], "w");
+ if (!out)
+ {
+ fprintf(stderr, "Error opening output file\n");
+ exit(1);
+ }
+ }
+ else if (argc == 2)
+ {
+ in = stdin;
+ out = stdout;
+ }
+ else