anchor.diff:  var num=0;
   List<String> club_picture=[];
   void main(){
  - /**for(int i=1;i<5;i++)
  + /*for(int i=1;i<5;i++)
    {club_picture[i]='club_picture/picture'+i.toString();
    }*/
   picture1=querySelector("#picture1");
  
positive.code:  querySelector("#next").onClick.listen(nbutton);
  }
  void lbutton(Event e){
    if(num==0) {alert('Ѿǰҳ');}
    else{
      num=num-4;
      picture1.src="club_picture[num]";
  
negative.code: 
  }
  void nbutton(Event e) {
  if(num!=5){
      num = num + 4;
      picture1.src="club_picture[num]";
      picture2.src="club_picture[num+1]";
      picture3.src="club_picture[num+2]";
      picture4.src="club_picture[num+3]";
    }
    else {
      alert('Ѿһҳ');
  