Quadratic equation in Fortran

Example for versions gfortran 4.5.0

This example uses built-in complex data type. 

program Quadratic
  integer a, b, c
  real d, p1, p2
  complex cp2

  read (*, *) a
  if (a.eq.0) then
    write (*, *) "Not a quadratic equation"
    stop
  end if
  read (*, *) b
  read (*, *) c
  d = b * b - 4 * a * c
  p1 = - b / 2.0 / a
  if (abs(d) < 1.0e-9) then
    write (*, "(A, F8.3)") "x = ", p1
  elseif (d > 0) then
    p2 = sqrt(d) / 2.0 / a
    write (*, "(2(A, F8.3))") "x1 = ", p1 + p2, char(13)//char(10)//"x2 = ", p1 - p2
  else
    cp2 = sqrt(cmplx(d)) / 2.0 / a
    write (*, "(2(A, F8.3, F8.3), A)") "x1 = (", p1 + cp2, ")"//char(13)//char(10)//"x2 = (", p1 - cp2, ")"
  end if
end