wc/wc.c

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

// STDIN_FILENO
int process_fn(int fn)
{
    char c[1];
    while (read(fn, c, sizeof(c)) > 0) {
        printf("%c", c[0]);
    }
		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("To do");

		}
    return 0;
}