709. 转换成小写字母

std::string Algorithm::toLowerCase(string str)
{
	string strNew;
	int nStr = str.length();
	for (int iStr = 0; iStr < nStr; iStr++)
	{
		char ch = str[iStr];
		if (ch >= 'A' && ch <= 'Z')
		{
			ch = ch + 32;
		}
		strNew.push_back(ch);
	}
	return strNew;
}