You need to test your apps with a fine tooth comb before putting them up for all to see. I would only put the ones that are completely dummy proof. Your calculator app does not show correct numbers when they get over the size of the display screen. Also, the calculator would not calculate 000.5 * 2. It really should not allow anyone to enter beyond one zero left of the decimal place (i.e. 0.5 * 2). For the voting app, I could not tell if my vote was cast. I could keep changing which radio button I selected and clicked the Vote button each time, but there was no message saying I could not do that or I needed to login to vote. There may be many more problems, but I think this will get you started in thinking about not only the best looking apps from a design stand point (you do a great job on that part), but also the user experience needs to be considered. Finally, the apps must work.