program simple_cannon
       integer pgopen
       if(pgopen('/xwin')<=0)stop
 
c Initial
       vx=1.0
       vy=1.5
       x =0.0
       y =1.0
       g = -9.8
       dt=0.0001 

       call pgenv(0.0,2.0,0.0,2.0,1,0)

c Euler algorithm
       do while(y>0.0)
         vx=vx
         x =x +vx*dt
         vy=vy+ g*dt
         y = y+vy*dt
         call pgpt(1,x,y,20)
       end do

       call pgclos
       end