Make iPhone switch automatically between Wi-Fi and cellular?

The reason I ask is because my University's Wi-Fi is very poor in some spots, so if I'm trying to access the internet, I have to go into settings, Wi-Fi, and turn Wi-Fi off, just so I can switch to 4G so I can actually get a connection. And then I have to switch it back if I think I'm in a place with a good Wi-Fi signal.
Is there any way to do this automatically? Like when I'm connected to Wi-Fi and can't get a connection, it will automatically switch to cellular. I believe I remember hearing that at the beginning of the iPhone 5 launch it did this, but people complained about it.

All iphones already do this.

No. If it detects Wi-Fi & uses that no matter how poor the signal, only if the Wi-Fi signal is non existant will it switch back to data.

I have somewhat the same issue but that's the way all smartphones work.