#include <cstdlib>
#include <iostream>
#include <fstream>
#include <string>
using std::string;

/*
 * Read the next unit from standard input.  Units are alternating all
 * alphanumeric, or non-alphanumeric.  No unit is empty; return the empty
 * string to indicate end of input.
 */
std::string read_next(std::istream &strm)
{
	// Read the first character.  If none, we're done.
	char firstch;
	if(!strm.get(firstch)) return "";

	// Result string.  Starts with that first character.
	string ret;
	ret.push_back(firstch);

	// Now, use the istream peek() method to add all immediately following
	// characters of the same class
	int nextch;
	bool should_be_alnum = isalnum(firstch);
	while((nextch = strm.peek()) != EOF) {
		if(should_be_alnum == (bool)isalnum(nextch))
			ret.push_back(strm.get());
		else
			break;
	}
	
	return ret;
}

/*
 * Test method that reads the input stream and prints each item 
 * surrounded by [].  Puts ten of them on a line, but some items contain
 * line breaks.
 */
const int LIMIT = 10;
void handle(std::istream &strm)
{
	string s;
	int cnt = 0;
	while((s = read_next(strm)) != "") {
		std::cout << "[" << s << "]";
		if(++cnt == LIMIT) {
			cnt = 0;
			std::cout << std::endl;
		} else {
			std::cout << " ";
		}
	}
}

/*
 * Attempt to open a file and run the test on it.
 */
void run_on_file(string fn)
{
	// Try to open a file to read.
	std::ifstream in(fn);
	if(!in) {
		std::cout << "Cannot open " << fn << std::endl;
		exit(1);
	}
	handle(in);
}

/*
 * Read from a file named on the command line, requested from the user,
 * or on standard input.
 */
int main(int argc, char **argv)
{
	/*
	 * See where we're getting our data from
	 */
	if(argc > 1) {
		// There seems to be a file name.
		if(string(argv[1]) == "-" || string(argv[1]) == "") {
			// Just read the standard input.
			handle(std::cin);
		} else {
			// Read the file from the command line.
			run_on_file(argv[1]);
		}
	} else {
		// Ask for a file name and run there.
		string fn;
		std::cout << "What file to read? ";
		std::getline(std::cin,fn);
		run_on_file(fn);
	}
}