Javascript math with negative values

[Emn1ty]

I am wondering if anyone has a method to deal with negative numbers in math equations for javascript. At the moment I will sometimes get negative numbers resulting from some math done, for example I take the maximum number value in a set of information, multiply it half and add that value back:

var maxLength = 100;
var minLength = 1;
var LengthBuffer = maxLength * .5;
var endLengthRange = maxLength + LengthBuffer ;
var startLengthRange = minLengthBuffer - LengthBuffer;


// The above should yield 150 and -49, the issue is in the next part.
// Due to needing to find a median between the end of this range and
// the start (which here should be 199/2) the following math does not work correctly

var lengthRange = endLengthRange - startLengthRange;


//this will return 101 and not 199.
[/CODE]

[Elliott]

In what browser? I tried it in Safari and lengthRange gets set to 199 (like you're expecting).

[Emn1ty]

I've been testing this in Chrome but I get the same answer in FF as well. I'll post the code up that I'm working with.

function randomFromTo(from, to){
	   return Math.round(Math.random() * (to - from + 1) + from);
	}
randomFromTo(10,20);  //18
randomFromTo(10,20);  //10
randomFromTo(10,20);  //15
randomFromTo(10,20);  //20
var carPrices = new Array();
var carMiles = new Array();
var allCars = new Array();
   for (i=0;i<400;i++) {  
	allCars[i] = new Array();
	allCars[i][0] = "car "+(i+1);
	allCars[i][1] = randomFromTo(1000,500000); //miles
	  allCars[i][2] = randomFromTo(5000,50000); //dollars  
	//document.write(allCars[i][0]+' Miles: '+allCars[i][1]+' Price $'+allCars[i][2]+'<br />')
   }





   totalMile = 0;
   totalPrice = 0;
   for(var i = 0; i < allCars.length - 1; ++i){
	 //document.write(totalMile+" + "+allCars[i][1]+" =");
   totalMile = totalMile + allCars[i][1];
   totalPrice = totalPrice + allCars[i][2];

   carMiles [i] = allCars[i][1];
   carPrices [i] = allCars[i][2];

	  //document.write(totalMile+'<br />');
	}
   //document.write(totalMile);
   var totalCars = allCars.length;

   var largestPrice = Math.max.apply(Math, carPrices);
   var largestMiles = Math.max.apply(Math, carMiles);
   var smallestPrice = Math.min.apply(Math, carPrices);
   var smallestMiles = Math.min.apply(Math, carMiles);

   var yourCar = new Array();
   yourCar[0] = new Array();
   yourCar[0][0] = 'car1';
   yourCar[0][1] = 20000;
   yourCar[0][2] = 25000;



   var bufferMiles = largestMiles*.5;
   var bufferPrice = largestPrice*.5;
  // document.write('Your car is '+yourCar[0][0]+' with '+yourCar[0][1]+' miles and is priced at $'+yourCar[0][2]+'<br />');
   var yourCarMiles = yourCar[0][1];
   var yourCarPrice = yourCar[0][2];
   var startPriceRange = smallestPrice-bufferPrice;
   var startMileRange = smallestMiles-bufferMiles;
   var averageMile = totalMile/totalCars;
   var averagePrice = totalPrice/totalCars;
   var mileRangeEnd = largestMiles+bufferMiles;
   var priceRangeEnd = largestPrice+bufferPrice;
   var mileRange = mileRangeEnd - startMileRange; // Does not yield correct value
   var priceRange = priceRangeEnd - startPriceRange; // Does not yield correct value
   var mileMedian = mileRange*.5;
   var priceMedian = priceRangeEnd*.5;
  //document.write('Average Price: $' + averagePrice +'<br />');
  //document.write('Average Mileage: ' + averageMile +'<br />');
  //document.write('number of cars: '+totalCars+'<br />');
  //document.write('Highest Mileage: '+largestMiles+'<br />');
  //document.write('Highest Price: '+largestPrice+'<br />');
  //document.write('Lowest Price: '+smallestPrice+'<br />');
  //document.write('Lowest Mileage: '+smallestMiles+'<br />');
  document.write(mileRangeEnd+' - '+startMileRange+' = '+mileMedian+'<br />');
  document.write('Middle Mile Range: '+priceMedian+'<br />');
  document.write('Middle Price Range: '+priceMedian+'<br />');
  document.write('Middle Mile Range: '+mileMedian+'<br />');
[/CODE]

[Elliott]

Well, I'm stumped. From both your example code and your actual code, I'm always getting the values you're expecting. For example, startPriceRange gets set to -19590. priceRangeEnd gets set to 74442. priceRange gets (properly) set to 94032.

Tested in Safari, Chrome, and Firefox.

Edit: Is this the part that's confusing you?:

document.write(mileRangeEnd+' - '+startMileRange+' = '+mileMedian+'<br />');[/CODE]

If I'm understanding this correctly, you should be outputting mileRange in that example, not mileMedian.

[Emn1ty]

I found the issue:

var mileMedian = mileRange*.5;
   var priceMedian = priceRangeEnd*.5;
//priceRangeEnd should be priceRange
[/CODE]