program pg_show
c
       integer pgopen, i
       real x(200), y(200), f, xmin,xmax,ymin,ymax, delta_x
       external f
c
       if (pgopen('/xwin').le.0) stop
c
       write (*,*) 'What is the range of x ?'
       read (*,*) xmin, xmax
c
c      write (*,*) 'What is the range of y ?'
c      read (*,*) ymin, ymax
c
       delta_x = (xmax-xmin)/200      
       do i=1,200
         x(i) = xmin + (i-1)*delta_x
         y(i) = f(x(i))
       end do
c
       ymin = y(1)
       ymax = y(1)
       do i=1,200
         if (y(i).gt.ymax) ymax = y(i)
         if (y(i).lt.ymin) ymin = y(i)
       end do
c
       call pgenv(xmin,xmax,ymin,ymax,0,1)
       call pgline(200,x,y)
       call pgclos
c
       end

c
       function f(x)
       real f, x
c      f = x**3
       f = 7*sin(x) + x
       end