Q: iPhoto has been deleted and I can't get it back

Hello,

I recently had a few issues with iPhoto where it would tell me that it was in use by another application or generally is not currently able to work. I decided to back up all of my photos before resolving the issue so I do have them all on a hard drive and Picasa but then I proceeded to try and fix iPhoto. It then went through a process where it retrieved all of my photos and videos but will not let me look at them when I double click. I decided to delete iPhoto off my computer and put it in the trash followed by emptying it, assuming I would be able to re-download it from the app store but it isn't there.. I can't find it anywhere and now I don't think I will be able to use that software again which is really annoying because it is the best software I have used for all of my photos and is one of the most vital parts of my macbook. The only evidence I have of it is the original icon on the bar at the bottom of the screen but it is faded and has a question mark over it! Anyone know how I could maybe find it to re-download it or another version? Thank you for reading!