this is the wrong
chkIos = (CheckBox) findViewById(R.layout.chkIos);
chkAndroid = (CheckBox) findViewById(R.layout.chkAndroid);
chkWindows = (CheckBox) findViewById(R.layout.chkWindows);
btnDisplay = (Button) findViewById(R.layout.btnDisplay);
change like this
chkIos = (CheckBox) findViewById(R.id.chkIos);
chkAndroid = (CheckBox) findViewById(R.id.chkAndroid);
chkWindows = (CheckBox) findViewById(R.id.chkWindows);
btnDisplay = (Button) findViewById(R.id.btnDisplay);