A sentinel loop looks like the best choice.
There are various ways to do this. One way is to have the user hit "enter" to continue after each set of roots has been printed, and "q" followed by "enter" to quit. User interaction will look something like this:
Enter a b c: 1 -2 -15 Two solutions: x = 5.000000 and x = -3.000000 Hit enter to continue, q enter to quit: Enter a b c: 1.0 0.0 -6.25 Two solutions: x = 2.500000 and x = -2.500000 Hit enter to continue, q enter to quit: Enter a b c: 0 4 5 Coefficient a must not be zero Hit enter to continue, q enter to quit: Enter a b c: 1.5 9.375 2.75 Two solutions: x = -0.308568 and x = -5.941432 Hit enter to continue, q enter to quit: Enter a b c: 2 1 1 No real roots Hit enter to continue, q enter to quit: q Bye!
Does the universal flow chart apply to this program?