学步园

 这是一道水题，主要是对字符串输入的判断以及空行的判断，一定要注意其空行的判断，而string.size（）==0并不代表着是空行！

#include "iostream"
#include "string"
using namespace std;
bool checkEmpty(string str)//检查这一行是不是空行   
{  
    for(int i = 0;i < str.size();++i)  
        if(str[i] > ' ') return false;  
    return true;  
}  
int main ()
{
	string str1, str2;
	while (1)
	{
		getline (cin, str1);
		getline (cin, str2);
		if (str2.size() != 0 && !checkEmpty(str2))
		{
			string str3, str4, str5, str6; 
			str3.assign(str2, 0, (str2.size()+1)/2);
			str4.assign(str2, str3.size(), str2.size()+1);
			str5.assign(str3.rbegin(), str3.rend());//将字符串倒转
			str6.assign(str4.rbegin(), str4.rend());
			cout << str5 + str6 << endl;
		}
		if (str1.size() != 0 && !checkEmpty(str1))
		{
			string str3, str4, str5, str6;
			str3.assign(str1, 0, (str1.size()+1)/2);
			str4.assign(str1, str3.size(), str1.size()+1);
			str5.assign(str3.rbegin(), str3.rend());
			str6.assign(str4.rbegin(), str4.rend());
			cout << str5 + str6 << endl;
		}
		if (cin.eof())  break;
	}
}