Delete problem with double at Calculator App at android studio?

I am trying make a calculator app in Android Studio. But i cant fix delete function problem. If the number is decimal,it can not deletes before the decimal comma. For example my number is (12,12). Delete button is first deleting last number, so new number is (12.1.). And later (12.) And later (12.). It is cant be (12) or (1). How can i fix ?

btnclear.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Value1 = Double.parseDouble(edttext.getText() + "");
            String s = Value1 + "";
            String Res = "";
            for (int i = 0; i < s.length() - 1; i++) {
                Res += s.charAt(i);
            }
            if (Res.equals(""))
                edttext.setText("0");
            else
                edttext.setText(null);
            edttext.setText(Res);
        }
    });