The Quadratic Formula

            2
   f(x) = Ax  + Bx + C = 0


 Find the "roots" of the above equation
   (i.e. where it crosses the x-axis)

 Write is function called compute_roots()
   that determines:

 (1) how many roots exist given A, B, C
   -- zero if it never crosses the x-axis
   -- one if it crosses the origin
   -- two if it crosses the x-axis twice
    HINT: this can be the return value

 (2) calculate the root(s)

 The user enters coefficients A, B, and C

 TEST CASES:
  A = 1   B = 0    C = 10  ==>  none
  A = 1   B = 0    C = 0   ==>  0
  A = 1   B = -5   C = 6   ==>  3 and 2