Wifi automatically connecting.

I've been an iPhone user since the 3g came out. Now i'm transitioning to Mac computers too. It seems my computer has automatically connected to many password protected wifi networks in my life. Now it seems my phone will do the same after connecting my computer to a network. Is this a feature I can turn off. I don't often connect my phone to public wifi because I have unlimited LTE and public wifi is often slower and less secure.