学到了stringstream的用法 还有s.scanf 注意头文件
```

include [HTML_REMOVED]

include [HTML_REMOVED]

using namespace std;
int main(){
string s,a,b;
getline(cin,s);
cin>>a>>b;
stringstream str(s);
string t;
while(str>>t){
if(t==a)cout<<b<<’ ‘;
else cout<<t<<’ ‘;
}
return 0;
}
```