Building Javascript Calculator

Question

I am trying to build a calculator in javascript but I am stuck and don't know how to proceed. every time someone click on 1 + 1 / 2, for exemple I am creating an array that pushes everything that was typed so in the case above the array would be

[1, "+", 1, "/", 2];

However, I can't figure it out how to transform this array into an actual mathematical value. I had an idea of looping through all elements like this:

for(var i=0; i<arrayCharacters.length ;i++){
            if(arrayCharacters[i] != "*" || arrayCharacters[i] != "/" || arrayCharacters[i] != "+" || arrayCharacters[i] != "*"){
                arrayNumbers.push(arrayCharacters.slice(0, i));
                console.log(arrayNumbers);
            }
        }

It's very incomplete because I got stuck. Can anyone help me?

You have to come up with your own interpretation of +, -, /, *.. operators. — webdeb
– webdeb, Commented Jun 26, 2017 at 17:36
Instead of inserting sequentially, you can try looking at RPN, which is used commonly to make calculators. — Scott
– Scott, Commented Jun 26, 2017 at 17:39

Jonas Wilms · Accepted Answer · 2017-06-26 18:08:37Z

var result=eval(arrayCharacters.join(""));

You could also parse the expression manually, however this requires building up a tree, as math isnt evaluated left to right.

If you really want to parse it on your own (which is far better then eval), you could use a math notation that really goes from left to right , so its much easier to parse ( As @Scott suggested). An implementation:

var stack=[];
var arrayCharacters=[1,2,"/",1,"+"];

for(var i=0;i<arrayCharacters.length;i++){

 var char=arrayCharacters[i];

 if(typeof char==="number"){
    stack.push(char);
    continue;
 }

 var op2=stack.pop()||0;
 var op1=stack.pop()||0;
 var res;

 if(char=="+"){
  res=op1+op2;
 }
 if(char=="-"){
  res=op1-op2;
 }
 if(char=="*"){
  res=op1*op2;
 }
 if(char=="/"){
  res=op1/op2;
 }

 stack.push(res);
}

var result=stack.pop();

Math Syntax (RPN (1)):

1+2 => 1 2 +
1/2+3 => 1 2 / 3 +
1+2/3 => 1 2 3 / + 
(1+2)/3 => 1 2 + 3 /
1/2/3+4/5/6 => 1 2 / 3 / 4 5 / 6 / +

http://jsbin.com/zofeqitiba/edit?console

Erick Lanford Xenes · Accepted Answer · 2017-06-26 17:59:45Z

1

"eval" function is a very good choice in your case. Also you can use the math.js library, which comes with a powerful expression parser.

http://mathjs.org

answered Jun 26, 2017 at 17:59

Erick Lanford Xenes

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