Thank you! I didn't try just rebooting first, but I cleared my data from the Camera (and the flashlight app for good measure) and then rebooted! I didn't have to take the battery out. My flashlight app now works. Thanks so much!
i couldn't find the Camera in my Apps, i'm using Huawei P6. However i figured out another way to fix this.
if anyone couldn't find the Camera in Settings>All Apps, you may go into your camera, open up the setting, and then look for "reset".
the camera will be fix! // don't worry, it will only reset your camera settings, you may change the setting for resolutions, etc back later.