Count Lines, Words & Chars (Linux wc) in C

#include <stdio.h>
#include <ctype.h>

int main (int argc, char **argv) {

    int c, in = 0;                      /* current char, in-word flag */
    size_t nc = 0, nw = 0, nl = 0;      /* count of chars, words, lines */
    /* use filename provided as 1st argument (default: stdin) */
    FILE *fp = argc > 1 ? fopen (argv[1], "r") : stdin;

    if (!fp) {  /* validate file open for reading */
        perror ("file open failed");
        return 1;
    }

    if ((c = fgetc (fp)) == EOF) {      /* read 1st char, validate */
        fputs ("empty-file.\n", stderr);
        return 1;
    }

    if (!isspace(c))                    /* if not space */
        in = 1;                         /* set in-word flag */
    nc++;                               /* increment char count */

    while ((c = fgetc (fp)) != EOF) {   /* read remaining chars in file */
        if (isspace(c)) {               /* if whitespace */
            if (in)                     /* if in-word (now 1-past end of word) */
                nw++, in = 0;           /* increment word count, clear in flag */
            if (c == '\n')              /* if newline */
                nl++;                   /* increment line count */
        }
        else if (!in)                   /* normal character & not in-word */
            in = 1;                     /* set in-word flag true */
        nc++;                           /* increment char count each iteration */
    }
    /* non-POSIX end-of-file check */
    if (in)                             /* if in at EOF (no POSIX eof) */
        nw++, nl++;                     /* increment word & line count */

    /* minic Linux wc output behavior */
    if (fp != stdin) {  /* not reading stdin, print filename */
        printf (" %zu %zu %zu %s\n", nl, nw, nc, argv[1]);
        fclose (fp);    /* close file if not stdin */
    }
    else    /* reading stdin, omit filename */
        printf (" %zu %zu %zu\n", nl, nw, nc);
}

/*

**Example Use/Output**

    $ ./bin/wc_wordcount < /var/lib/dict/words
     305089 305089 3137778

*/