新手，关于cin读取string的问题

string a,b;
while(cin>>a)
{
if(b==a)

 break;
else
{
b=a;
}
}
if(a==b&&!a.empty())
cout<<a<<endl;
else
cout <<"no";

用这段程序来判断输入的字符串中是否有连续的两个字符串相等，怎么输入才能实现
[解决办法]

# include <iostream>
# include <string>

using namespace std;

int main()
{
    string a, b;
    while (cin >> a)
    {
        if (b == a)
            break;
        else
            b = a;
    }
    if (a == b && cin)
        cout << a << endl;
    else
        cout << "no" << endl;

    return 0;
}