My iPhone 4s camera is frozen?

I tryed to take a selfie and the screen just stayed on a black image! I can flip to different things on the camera thing like the square camera options and others but it stays on a black image and I can't take a picture from the back or the front! I'm so

I have ties same phone an mine does hat all the time. Just double click your home button and swipe the camera app up. Or try Turing it on and off again. Works for me.