Arduino DUE - Input (digitalRead) problem

Hello I am new here and new with DUE. I have a Due and I was using Pins 5,6,6 as an input. I set the pinMode in the setup block. I have pushbuttons that send 3.3V when it's pressed.But output pins are high all the time. I can get outputs to LOW, only if I directly connect inputs to ground. On UNO program work normally.
What should I do. I just want to set output HIGH when on input is 3.3V(pushbutton)

Thank you for HELP.

Hello Mravlak,

Use a 10K external pull down resistor between the input and ground
and

pinMode(pin, INPUT_PULLUP);

-p