program problem_1
c This program will draw y=sin(x) using pgplot routines. 
      real y(100), x(100), delta_x
      integer i, pgopen
      delta_x = 4.0*3.14159/100.0
      if (pgopen('?').le.0) stop
      do i=1, 100
        x(i) = (i-1)*delta_x
        y(i) = sin(x(i))
      end do
      call pgenv(0.0, 12.0, -2.0, 2.0, 0, 1)
      call pglab('x','y', 'y=sin(x)')
      call pgline(100, x, y)
      call pgclos
      end