68   int argi;  in main()  local
70   for (argi = 1; argi < argc; argi++)  in main()
72     if (argv[argi][0] == '-')  in main()
74       switch (argv[argi][1])  in main()
81           argi++;  in main()
82           if ((fp_al = fopen (argv[argi], "rb")) == NULL)  in main()
86                argv[argi]);  in main()
97           fprintf (stderr, "Error:  unknown option %s\n", argv[argi]);  in main()
105       if ((fp_rd = fopen (argv[argi], "rb")) == NULL)  in main()
108         fprintf (stderr, "Error:  file %s does not exist\n", argv[argi]);  in main()
114       if ((fp_wr = fopen (argv[argi], "wb")) == NULL)  in main()
117         fprintf (stderr, "Error:  can not create PNG-file %s\n", argv[argi]);  in main()