C++ n00b question

I don´t understand the following code, particularly how the next string is stored into "previous". "cin>>current" just moves words into current. Where is the order to move the next word into previous? Code is from Stroustup:

[code]
int main()
{
   string previous = " ";
   string current;
   while (cin>>current){
      if(previous==current)
         cout<<"word repetition:"<<current<<'\n';
      previous=current;
   }
}

[/code]

previous=current;