program square_rot_anim
      real x(5),y(5),xnew(5),ynew(5),xold(5),yold(5)
      write(*,*)'drgrees for rotation?'
      read(*,*)n
      idummy=pgopen('/xwin')
      call pgenv(-10.0,10.0,-10.0,10.0,1,0)

      x(1)=2
      y(1)=2
      x(2)=2
      y(2)=-2
      x(3)=-2
      y(3)=-2
      x(4)=-2
      y(4)=2
      x(5)=x(1)
      y(5)=y(1)

      do i=1,5
        xold(i)=x(i)
        yold(i)=y(i)
      end do

      d_theta=2*3.14159/360
      theta=n*d_theta
   
      do j=1, 100000
  
        theta=theta+0.01*d_theta

        do i=1,5 
          xnew(i)=x(i)*cos(theta)-y(i)*sin(theta)
          ynew(i)=x(i)*sin(theta)+y(i)*cos(theta)
        end do

       call pgbbuf
        call pgsci(0)
        call pgline(5,xold,yold)
        call pgsci(1)
        call pgline(5,xnew,ynew)
       call pgebuf

        do i=1,5
          xold(i)=xnew(i)
          yold(i)=ynew(i)
        end do

      end do

      call pgclos

      end