Question

I’m working on a ‘Equation Calculator’ but have a few problems. I can now insert my equation but I want it to be numbers, but not just numbers: I want all the ‘+’ ‘s, the ‘-‘ ‘s, the ‘*’ ‘s and the ‘/’ ‘s to be the right things.

So here is my code until now:

---

var ligning = prompt("Insert your equation here:");
var newLigning = ligning.split("=");
var sideOne = parseInt(newLigning[0],10);
var sideTwo = parseInt(newLigning[1],10);
var calculator = function() {

};
alert(sideOne);
alert(sideTwo);

---

To be very specific here is an example:

‘1 + 2 = 3’ should alert 3 and then 3 again (because of the two alerts down in the bottom) – How can I make that?

Answer 1

Instead of :

var sideOne = parseInt(newLigning[0],10);

You might want to have something of the sort :

var sideOne = performMath(newLining[0],10);

Where :

function performMath(equation) {
    //CODE HERE
}

performMath could be done in a few ways. You need to split the equation and obtain the numbers and the equations between the 2. This can be done recursively!

I think this could be a good starting point.

Edit

Unraleted to the question, if you start taking the operation priority (PEDMAS) into account this is a slightly harder task. The approach is the same, performMath would need to be slightly more complexe. In such a case, I would recomend some sort of array structure for the numbers and another for the equations.

Edit 2

Paul S Also made a good point of sanitising the string before getting started. You cannot assume someone will enter an equation. When programming Rich Cook said:

“Programming today is a race between software engineers striving to
build bigger and better idiot- proof programs, and the Universe trying
to produce bigger and better idiots. So far, the Universe is winning.”

Edit 3

This little snippet of code should be somewhat helpful… by all means this might not the most efficient code…

var equation = "1+22-3";
var operators = "+-*\/"

var currentNumber = "";
var numbers = new Array();
var operatorArray = new Array();
for(var i=0; i<equation.length; i++) {
  var currentChar = equation.charAt(i);
  if(operators.indexOf(currentChar) != -1) {
    operatorArray[operatorArray.length] = (currentChar);
    numbers[numbers.length] = (currentNumber);
    currentNumber = "";
  } else {
    currentNumber = currentNumber + currentChar;
    alert(currentNumber);
  }
}
numbers[numbers.length] = currentNumber;
alert("numbers : " + numbers);
alert("operators : " + operatorArray);

Now all you have to do is go through the arrays and perform the proper operations.