"No implicit type" error for init_window

Thanks Jeff for solving my last problem.
Now, when I declare a graphics window, I get a compiler error: "No implicit type" on the init_screen line. It also says: Error: Keyword argument requires explicit interface for procedure 'init_screen'

program main
use appgraphics
implicit none
    integer::screen
    integer::x, y, r, i         
    x=10
    y=10
    r=1   
    screen = init_screen(800, 600, title="Draw Primitives")     
    call settextstyle(2,0,5)   
    do while(x <= 800)
      call clearviewport 
      call circle(x,y,r)
      call outtextxy(x,y,char(r),pt)
      i=0
      do while(i < 100000)
         i=i+1
      end do
      x=x+25
      y=y+15
      r=r+12
    end do
    call delay(1)
    call closewindow(screen)
end program main