wc/wc.c

#include <stdio.h>
#include <unistd.h> // read, isatty

// STDIN_FILENO
int process_fn(int fn)
{
    char c[1];
		int seen_word=0;
		int seen_sep_after_word=0;
		int num_words = 0;
    while (read(fn, c, sizeof(c)) > 0) {
				if(*c != '\n' && *c != ' ' && *c != '\t'){
					seen_word = 1;
				} else if(seen_word) {
					seen_sep_after_word = 1;
				} else {
					// see a separator, but haven't seen a word: do nothing
					// exercise: what happens if you only track seen_sep,
					// instead of seen_sep_after_word?
					// test with: $ echo " x x" | ./wc
				}
				if(seen_word && seen_sep_after_word){
					num_words++;
					seen_sep_after_word = seen_word = 0;
				}
    }
		if(seen_word){
			num_words++;
		}
		printf("%i\n",num_words);
    return 0;
}

int main(int argc, char** argv)
{
    if (!isatty(STDIN_FILENO)) {
        return process_fn(STDIN_FILENO);
    } else if (argc > 1) {
        FILE* fp = fopen(argv[1], "r");
        if (!fp) {
            perror("Could not open file");
            return 1;
        }
        return process_fn(fileno(fp));
    } else {
        printf("Usage: ww file.txt\n");
				printf("   or: cat file.txt | ww\n");
    }
    return 0;
}