stringstream类

# include <iostream>
# include <cstring>
# include <sstream>
using namespace std;
int main()
{
    string s,S,str;
    int cnt=0;
    getline(cin,s);
    s=s.substr(0,s.size()-1);
    stringstream ssin(s);
    while(ssin>>str)
    {
        if(str.size()>cnt)
        {
            cnt=str.size();
            S=str;
        }
    }
    cout<<S<<endl;
    return 0;
}