#define _POSIX_C_SOURCE 200809L

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
  FILE * current_input_file;
  int i; char c;

  int using_unbuffered_output;

  int error_occurred;

  for(i = 1; i < argc; i++) {
    if(argv[i][0] == '-') {
      if(argv[i][1] == 'u') {
	using_unbuffered_output = 1;
	i = argc;
      }
    }
  }

  if(argc == 1) {
    current_input_file = stdin;
    for(c = fgetc(current_input_file); c != EOF;
	c = fgetc(current_input_file)) {
      if(using_unbuffered_output) {
	write(1, &c, 1);
      }
      else {
	fprintf(stdout, "%c", c);
      }
    }
    fclose(current_input_file);
  }
  
  for(i = 1; i < argc; i++) {
    if(argv[i][0] == '-' && argv[i][1] == '\0') {
      current_input_file = stdin;
    }
    else if(argv[i][0] == '-' && argv[i][1] == 'u' &&
	    argv[i][2] == '\0') {
      if(argc > 2) {
        continue;
      }
      else {
	current_input_file = stdin;
      }
    }
    else {
      current_input_file = fopen(argv[i], "r");
      if(current_input_file == NULL) {
	fprintf(stderr, "%s: %s: No such file or directory\n",
		argv[0], argv[i]);
	error_occurred = 1;
      }
    }
    for(c = fgetc(current_input_file); c != EOF;
	c = fgetc(current_input_file)) {
      if(using_unbuffered_output) {
	write(1, &c, 1);
      }
      else {
	fprintf(stdout, "%c", c);
      }
    }
    fclose(current_input_file);
  }

  if(error_occurred) {
    return 1;
  }
  else {
    return 0;
  }
}