string + string
#include<iostream>
using namespace std;
int main(void)
{
string s,sap;
cin>>s;
cin>>sap;
//s+=sap; //方法一
//s.append(sap); //方法二
cout<<s<<endl<<s.length()<<endl;
}
string1 = string2
#include<bits/stdc++.h>
using namespace std;
int main(void)
{
int n;
string s,sl;
while(cin>>s)
{
sl = s; //string 复制
cout<<s<<endl;
cout<<sl.append(s)<<endl; //string 尾加
cout<<(sl+=s)<<endl; //string 尾加
}
}