Recently I discovered, that via QPython console I can execute android (linux) commands. Ping works. Question is: how to interrupt it's output on smartphone? CTRL + C obviously isn't the answer.
Vol Down + C is functionally equivalent to Ctrl + C.
There may be a way to send the modifier keys through the terminal app, however I have never used that app so I can't say. On Terminal Emulator you can long press the screen and send the control key from the pop up menu.
Also you could install Hackers Keyboard which includes a full desktop keyboard including control and alt keys.
Most Term Emus use Vol Dn as Ctrl and use Vol Up as Fn. So in your case simply hold the Volume Down key and then press C on your keyboard (essestially, any IME works).