4[完成题]
 在下面的横线处填上适当内容，使程序完整。

   # include<iostream.h>

   # include<math.h>

   class loc{

         private:

                float x,y;

   public;

                loc()

                {float x1,float y1；

                   x=x1;

                   y=y1;

                }

                float getx( ){return x;}

                float gety( ){return y;}

                ②              float dis(loc&,loc&);

   };

   float loc::dis(loc&a,loc&b)

   {

         flost dx=a.x-b.x;

         flost dy=a.y-b.y;

         return sqrt(dx*dx dy*dy);

   }

   void main( )

   {

        loc pl(3.5,4.5),p2(5.5,6.5);

        float d=loc::dis(p1,p2);

        cout<<“The distance is”<<d;

   }