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