Can't figure out how to solve the decimal point bug in this calculator code

Question

Hi guys, I'm new in flash and is currently learning how to build a simple calculator with multipliers (plus,minus,multiple,divide,decimal point and change sign) but I'm stuck on the decimal point and change sign.
var multiplier_old:Number = 10;
var multiplier_new:Number = 1;
// .: Sets the multipliers so that new input numbers become decimals of a lower unit column
action_point.addEventListener(MouseEvent.MOUSE_DOWN, function():void {
          multiplier_old = 1;
          multiplier_new = 0.1;
          point = true;
// Takes intput from the input_ buttons and adds it to the input after applying the multipliers.
// If `point` is true then the multiplier_new is divided by 10, also as described.
function inputNumber(n:Number):void {
          input = input * multiplier_old + n * multiplier_new;
                    if (point) {
                                    multiplier_new *= 0.1;
                   trace(multiplier_new);
          output_txt.text = input.toString();
Decimal point
The problem is that when I input 2.7 in the calculator, it will display the values in output_txt correctly. But then when I input 2.78, it will display 2.780000000000000000000000002. This will also happen to other numbers if the input is too big.
What I want is just 2.78. How do I change the codings to make 2.780000000000000000000000002 become 2.78?
Change sign
Any tips on how to start on this one?
Thanks for your time,
Zainu

Answer 1

I think you misunderstand what I mean. The weird decimal doesnt comes out after I press the 'equals' sign. It comes out when im just pressing on the caculator number buttons
First I click the no.2 button and then the decimal point button.
So the caculation output display will show
2.
after that I press the no.7 button
2.7
and then no.8 button. It appears like
2.7800000000000000002
This is the code I use when the user press the decimal point button.
// .: Sets the multipliers so that new input numbers become decimals of a lower unit column
action_point.addEventListener(MouseEvent.MOUSE_DOWN, function():void {
          multiplier_old = 1;
          multiplier_new = 0.1;
          point = true;
// Takes intput from the input_ buttons and adds it to the input after applying the multipliers in the method described above.
// If `point` is true then the multiplier_new is divided by 10, also as described.
function inputNumber(n:Number):void {
          input = input * multiplier_old + n * multiplier_new;
                    if (point) {
                             trace(multiplier_new.toFixed(3));
                              multiplier_new *= 0.1;
                              //trace(multiplier_new);
          output_txt.text = input.toString();
I think there is some code wrong in this function that makes this weird problem. I tried putting toFixed method but it's still not working.
Sorry for this long reply but I have to try my bestto explain with my bad english.