71   int argi;  in main()  local
73   for (argi = 1; argi < argc; argi++)  in main()
75     if (argv[argi][0] == '-')  in main()
77       switch (argv[argi][1])  in main()
84           argi++;  in main()
85           if ((fp_al = fopen (argv[argi], "rb")) == NULL)  in main()
89                argv[argi]);  in main()
100           fprintf (stderr, "Error:  unknown option %s\n", argv[argi]);  in main()
108       if ((fp_rd = fopen (argv[argi], "rb")) == NULL)  in main()
111         fprintf (stderr, "Error:  file %s does not exist\n", argv[argi]);  in main()
117       if ((fp_wr = fopen (argv[argi], "wb")) == NULL)  in main()
120         fprintf (stderr, "Error:  can not create PNG-file %s\n", argv[argi]);  in main()