 # How to prevent the history from disappearing in Calculator

How to prevent the history from disappearing in Calculator
0

#1

I’m building a FreeCodeCamp Calculator. It’s almost finished. I just need to polish up several things. However, the main problem that is bothering me is why did the history area disappear when I press a number…

I tried to code the calculator in a way in which one person presses several numbers, and then presses a operator such as “x”, “+”, etc, the number already entered moves down to the history area. I’ve noticed that when I click on more than one number, the zero disappears. It’s also the same for when I click on a decimal “.”. In the case of the decimals, in first scenario, if I press “.”, the zero didn’t disappear but then I press a number, the zero disappears. In second scenario, if I press a number first, and then press a decimal, the zero disappears. I will list out the scenarios that I’ve experienced.

1. I pressed first number, the zero in the history area didn’t disappear. But when pressing the second and following numbers and decimals, the zero disappears. However, when I presses the operator and the numbers afterward, the history doesn’t disappear. So it means that the zero disappear for the first set before the operator.

2. I pressed the decimal. The zero doesn’t disappear. But when pressing a number or decimal next (I will fix the repeating decimals problem later), the zero disappear. But then after pressing the operator and numbers afterward, the history doesn’t disappear.

How do I fix it?

Here’s my Javascript/JQuery code from Codepen:

``````\$(document).ready(function() {

var mainMath = "0";
var subMath = "0";
var reset = "";
update();

\$("button").click(function(){
calculate(\$(this).attr("value"));
});

function calculate(keyitem) {
switch(keyitem) {
case "clear":
clearScreen();
break;
case "plusminus":
plusminusScreen();
break;
case "%":
percentageScreen();
break;
case "/":
case "*":
case "+":
case "-":
break;
case "0":
case "1":
case "2":
case "3":
case "4":
case "5":
case "6":
case "7":
case "8":
case "9":
break;
case ".":
break;
case "=":
solveEqual();
break;
}
update();
};

function clearScreen() {
mainMath = "0";
subMath = "0";
};

function plusminusScreen() {
mainMath = -1 * mainMath;
};

/*if (keyitem == "."){
if(mainMath == "0") {
mainMath = "0" + keyitem;
return;
}
}*/
if (mainMath == "0"){
mainMath = keyitem;
return;
}
if (subMath == "0") {
subMath = "";
}
mainMath+=keyitem;
};

if(mainMath == "0"){
subMath += "0";
}
subMath += mainMath;
mainMath = "0";
};

if (keyitem == "."){
if(mainMath == "0") {
mainMath = "0" + keyitem;
subMath = "0";
return;
}
}
};

function solveEqual() {
mainMath = eval(subMath+mainMath);
};

function update(){
\$("#history").html(subMath);
};

});
``````

#2

Becasue of this in `addNumber()`:

``````if (subMath == "0") {
subMath = "";
}
``````

every time you run `addNumber` it resets `subMath` to an empty string, because subMath is initialized at 0 it never gets a chance to receive any other number before it is cleared out.

#3

Yes, I do realize that it’s part of this problem. However, without this line, the zero is added to the first set of the numbers in the History area… I’m just trying to figure out what is the best solution…

#4

I solved this zero problem!

Here’s the solution in which I moved this code:

``````if(subMath == "0"){
subMath = "";
}
``````

to `function addOperator();`

#5

** I was typing this before i saw that you solved your problem
one solution

``````if (subMath === "0" && subMath.length===0) {
subMath = "";
}
``````

in other words, ensure that subMath already has some length before assigning any values to it ,
again this just a solution not necessarily the solution, looking at the remainder of your code thoroughly may yield other solutions

#6

That’s a good solution too! Thanks so much for your help in pointing out that this line might be half problem/half solution!

Right now, I’m solving the repeating decimal problem…