When I zoom the camera is out of focus - Canon PowerShot SD850 IS Digital Camera

I would consider focus shift when zooming normal. Most small digital camera zoom lenses do that. If your auto-focus is slow, all I can suggest is patience or a newer/better camera.

When you change the zoom, chances are the camera lose focus, and you need to half-press the shutter button again to the camera autofocus.

Its normal behavior to lose focus when zooming in or out.

Zoomed fully in, the minimum focus is about 20 inches. If you want to focus closer, you must zoom out. See page 72 of this manual.

change auto focus to single focus mode,
since it is on continuous auto focus on default, it would focus all the time so you don't need to click half way before taking a picture

No, your camera does not have a manual focus button.
Even if it did, you wouldn't be able to keep focus while zooming.
Only very expensive lenses maintain focus regardless of focal lenght.
The correct procedure is to zoom and then focus.

Its an error code and shows problem of Lens mechanism.
Lens focus / zoom motor is stuck that's why camera gives out of focus image.
You need to replace Lens Assembly and it would cost you more then camera worth.

double check that its still in auto focus, i went a whole day trying to figure out why my camera wouldnt focus, and i had auto focus off

I am sure your lens is clean but from what you describing you have a definte problem with the lens assy which includes the autofocus sensors. Sometimes is can be a faulty focus motor , dirt between sensor and outer lens. Camera needs to be stripped and checked up.

Tom, It's best to do the zoom first, then focus (if you are using the autofocus).

On a D-580 Zoom camera, the Macro Mode operating range is 8 inches to 20 inches. This means the camera must be between 8 inches and 20 inches away from the subject for a picture to be in focus.