i have problem with moving spheres at the same time on screen

Hello,
i have problem with my code which makes spheres at the same time moving from bottom to top of the page
the problem is the spheres doesn’t appear at a continues way or when multi sphere appear at the same time on the screen it appear and disappear
i don’t want that i want the spheres to appear in a continues way or nearly continues
in my code when i press ‘g’ buttons it generate a new sphere object in the screen the max possible spheres at the same time on the screen is 10 spheres
unfortunately i can’t figure out what is the problem so can you please help me or tell me another way to do it ,
this is my code jmq43h - Online C++ Compiler & Debugging Tool - Ideone.com .
Thanks in advance.