int StringToInt(string s)
{
	// This function converts from string to int.
	// It removes the leading and trailing space.
	// Note: There is a similar function in C++.
	int n = 0, len, i, m, count = 0;;
	char c;
	// Remove leading space
	len = s.size();
	for (i = 0; i < len; i++)
		if (s[0] == ' ')
			s = s.substr(1,s.size() - 1);
		else
			break;
	// Remove trailing space
	len = s.size();
	for (i = len - 1; i >= 0; i++)
		if (s[s.size() - 1] == ' ')
			s = s.substr(0,s.size() - 1);
		else
			break;
	len = s.size();
	i = len - 1;
	while (i >= 0)
	{
		count++;
		c = s[i];
		if (c >= '0' && c <= '9')
		{
			m = c - 48;
			n = n + m * pow(10,count - 1);
			cout << "count = " << count << " and " 
				<< n << endl;
		}
		else
		{
			cout << "Invalid character.\n";
			exit(1);
		}
		i--;
	}
	return n;
}