#include <iostream>
#include <string>

using namespace std;
string str;
void reverse(int begin,int end)
{
    while(begin<end)
    {
        str[begin] = str[begin]^str[end];
        str[end] = str[begin]^str[end];
        str[begin] = str[begin]^str[end];
        begin++;
        end--;
    }
}
int main()
{
    int i,j;
    while(getline(cin,str))
    {
        int len = str.length();
        int begin,end;
        i = 0;
        while(i<len)
        {
            begin = i;
            while(i<len&&str[i]!=' ')
                i++;
            end = i-1;
            reverse(begin,end);
            i++;
        }
        reverse(0,len-1);
        cout << str << endl;
    }
    cout << "Hello world!" << endl;
    return 0;
}

例如：I am zhang san.   输出：san. zhang am I;

笔试的一道题（字符串反转poj3750）