#include<iostream>
#include<string>
using namespace std;
 int main()
{
 string s1("ABC"),s2("DEF");
 if(s1==s2)
  cout<<"兩個字符串相同"<<endl;
 else
  cout<<"兩個字符串不相同"<<endl;
 s1+=s2;//字符串連接
 cout<<"連接之后的字符串是："<<s1<<endl;
 cout<<"連接之后的字符串的有效長度是："<<s1.size()<<endl;
 s1=s2;
 cout<<"復制之后的字符串是："<<s1<<endl;
 return(0); 
}