Ways of effectively Closing any and/or all apps

One problem I often having with using an I-Phone is effectively closing or getting out of apps. I would like to have an app that would enable me to close any app that I am using with a quick button. It is disconcerting when apps won't close and remain open once you go t another app. Every app should have a way out that is easy. I would put a close or exit any app I am in and want to exit. I would also put a button on phone desktop that would allow me to close current or all apps or have all apps close upon shutdown. Is this possible or could an app be written to accomplish this task? le