Thread: Exercise 5.10 (ACCELERATED C++)

Hi, I don't know how to stop the message "The longest palidrome is" from appearing if the user doesn't enter anything (just entering EOF). Where should I put that phrase? I'm not sure enough about the meaning of try-catch stuff. Thanks a lot...

Code:

/*
	Write a program to (1) find all the palindromes in a dictionary and (2) find the longest palindrome
*/
#include <iostream>
#include <string>
#include <vector>
#include <stdexcept>
#include <algorithm>
using namespace std;

vector<string> read_words(string&);
bool found(const string&);

int main()
{
	cout << "Enter some words: " << endl;
	string s;
	try {
		vector<string> myvec = read_words(s);
		vector<string>::iterator it = myvec.begin();
		while (it != myvec.end()) {
			if (found(*it)) {
				cout << *it << " ";
				++it;
			}
			else {
				it = myvec.erase(it);
			}
		}
		cout << endl;
		cout << "The longest palidrome is ";
		string::size_type maxlen = 0;
		string longest;
		for (int i = 0; i != myvec.size(); ++i) {
			if (myvec[i].size() > maxlen) {
				maxlen = max(maxlen, myvec[i].size());
				longest = myvec[i];
			}
		}
		cout << longest << endl;

	} catch (domain_error e) {
		e.what();
	}

	return 0;
}

vector<string> read_words(string& s)
{
	vector<string> v;
	while (cin >> s)
		v.push_back(s);

	typedef vector<string>::size_type vec_sz;
	vec_sz size = v.size();
	if (size == 0)
		throw domain_error("Empty vector");

	return v;

}

bool found(const string& s)
{
	bool found = true;
	for (string::const_iterator i = s.begin(), j = s.end() - 1; i < j; ++i, --j) {
		if (*i != *j)
			found = false;
	}
	return found;
}

If the user enters no text, but an immediate EOF, the line "The longest palindrome is: " is not printed. If you change your catch to be

Code:

cout << e.what();

then you'll see "Empty vector" printed instead.