Yes. If you have Ask to Join Networks on. It's easy to turn off as well. Read below.

Joining a Wi-Fi Network

The Wi-Fi settings let you turn on Wi-Fi and join Wi-Fi networks.

Turn on Wi-Fi:

Choose Settings > Wi-Fi and turn Wi-Fi on.

Join a Wi-Fi network:

Choose Settings > Wi-Fi, wait a moment as iPhone detects networks in range, then select a network (fees may apply to join some Wi-Fi networks). If necessary, enter a password and tap Join (networks that require a password appear with a lock icon ).

Once you’ve joined a Wi-Fi network manually, iPhone automatically connects to it whenever the network is in range. If more than one previously used network is in range, iPhone joins the one last used.

When iPhone is connected to a Wi-Fi network, the Wi-Fi icon in the status bar at the top of the screen shows the connection strength. The more bars you see, the stronger the connection.

Source Screenshots are mine