[RESOLVED] Help with maths in javascript

[chris1990]

I have created a instant taxi quote calculator, the function below is the code that is used to calculate the fare from the distance. The problem is i've got my self confused about the maths in particular the < and >. If you do the maths on an normal calculator with the distance as 1.08, the fare should be 2.34

distance = 1.08
distance - 1 = 0.08
0.08 * 1.80(PPM) = 0.144
0.144 + 2.20(FirstMile) = 2.344
fare = 2.34

When you run the fare calculator it calculates the fare at: 3.24, when i comment out the if statements and have the FirstMile at 2.20 and PPM at 1.80 it works as it should.

Thanks in advance, Chris1990

function calcFare() {
// variables
	var fareResult;
	var distance = document.getElementById('txtDistance').value;
 	var firstMile;// = 2.20;// 2.20 for 1st mile
	var pricepMile;// = 1.80;// 1.80 per mile
	var TrafficP;// = 1.00;// add 15% for traffic
 //	Select Tarrif

	if (distance > 15); // less than 15 Mile
	{firstMile = 2.20; // FM £2.20
	TrafficP = 1.00;// add 00% for traffic
	pricepMile = 1.80};// PPM £1.80 - standard tariff
	
	if (distance > 30); //less than 30 Mile
	{firstMile = 3.00; // FM £2.50
	TrafficP = 1.00;// add 15% for traffic
	pricepMile = 1.40};// PPM £1.40

 	if (distance > 50); // less than 50 Mile
	{firstMile = 3.00; // FM £3.00
	TrafficP = 1.00;// add 10% for traffic
	pricepMile = 1.30;}// PPM £1.30
	
	if (distance > 100); // less than 100 Mile
	{firstMile = 3.00; // FM £3.00
	TrafficP = 1.00;// add 10% for traffic
	pricepMile = 1.20;}// PPM £1.20
	
 	if (distance > 175); // less than 250 Mile
	{firstMile = 3.00; // FM £3.00
	TrafficP = 1.00;// add 10% for traffic
	pricepMile = 1.15;}// PPM £1.10
	
 	if (distance > 300); // less than 500 Mile
	{firstMile = 3.00; // FM £3.00
	TrafficP = 1.05;// add 10% for traffic
	pricepMile = 1.10;}// PPM £1.00
/*	
 	if (distance > 60); // Over 50 Mile
	{firstMile = 3.50; // FM £3.50
	TrafficP = 1.10;// add 10% for traffic
	pricepMile = 1.20;}// PPM £1.20
*/
  // calculator for Car
  		//exc 1st mile and calc rest of miles by PPM
  	fareResult = (distance - 1) * pricepMile
  		//inc first mile
  	fareResult = fareResult + firstMile;
  	//add percent for traffic
    fareResult = fareResult * TrafficP;	
  // show fare result
	var roundedNumber = roundNumber(fareResult,2);
		if (roundedNumber < 1.675) {roundedNumber = "1.70"};	
	document.getElementById('txtFare').value = roundedNumber;
	calcType();
	document.getElementById('btnBookNow').style.visibility='visible'; // show booknow button 
	}

[Zach_VB6]

Try this:

function calcFare() {
// variables
	var fareResult;
	var distance = document.getElementById('txtDistance').value;
 	var firstMile;// = 2.20;// 2.20 for 1st mile
	var pricepMile;// = 1.80;// 1.80 per mile
	var TrafficP;// = 1.00;// add 15% for traffic
 //	Select Tarrif

	if (distance <= 15) // less than 15 Mile
	{firstMile = 2.20; // FM &#163;2.20
	TrafficP = 1.00;// add 00% for traffic
	pricepMile = 1.80};// PPM &#163;1.80 - standard tariff
	else if (distance <= 30) //less than 30 Mile
	{firstMile = 3.00; // FM &#163;2.50
	TrafficP = 1.00;// add 15% for traffic
	pricepMile = 1.40};// PPM &#163;1.40
	else if (distance <= 50) // less than 50 Mile
	{firstMile = 3.00; // FM &#163;3.00
	TrafficP = 1.00;// add 10% for traffic
	pricepMile = 1.30;}// PPM &#163;1.30
	else if (distance <= 100) // less than 100 Mile
	{firstMile = 3.00; // FM &#163;3.00
	TrafficP = 1.00;// add 10% for traffic
	pricepMile = 1.20;}// PPM &#163;1.20
	else if (distance <= 175) // less than 250 Mile
	{firstMile = 3.00; // FM &#163;3.00
	TrafficP = 1.00;// add 10% for traffic
	pricepMile = 1.15;}// PPM &#163;1.10
	else if (distance > 300) // less than 500 Mile
	{firstMile = 3.00; // FM &#163;3.00
	TrafficP = 1.05;// add 10% for traffic
	pricepMile = 1.10;}// PPM &#163;1.00
/*	
 	else if (distance > 60) // Over 50 Mile
	{firstMile = 3.50; // FM &#163;3.50
	TrafficP = 1.10;// add 10% for traffic
	pricepMile = 1.20;}// PPM &#163;1.20
*/
  // calculator for Car
  		//exc 1st mile and calc rest of miles by PPM
  	fareResult = (distance - 1) * pricepMile
  		//inc first mile
  	fareResult += firstMile;
  	//add percent for traffic
    fareResult = fareResult * TrafficP;	
  // show fare result
	var roundedNumber = roundNumber(fareResult,2);
	if (roundedNumber < 1.675) {roundedNumber = "1.70";}
	document.getElementById('txtFare').value = roundedNumber;
	calcType();
	document.getElementById('btnBookNow').style.visibility='visible'; // show booknow button 
}

It'd help if you posted what should happen in English and then we can try to write it for you

[chris1990]

thanks for your help, sorry i thought i made it clear that the fare calculator was for some reason giving an incorrect fare of &#163;3.24 based on a distance of 1.08 miles. If you do the maths on a normal calculator, it will give the correct fare of &#163;2.34.

I tried using the code in your reply, but it stops the google map plugin on the page from loading. I have a working version of the fare calculator here, this version is based on the standard fare only (2.20 - first mile, 1.80 per mile). I am trying to implement a lower fare based on a larger distance.

thanks chris1990

[chris1990]

As you can see i've reversed the code, using the fare calculator with a distance of 1.08 miles now correctly displays a price of &#163;2.34. However when using a larger distance such as 195.14 miles its displays a price of &#163;351.65, when it should be &#163;226.26

thanks chris1990

 	if (distance <= 300); // less than 300 Mile
	{firstMile = 3.00; // FM &#163;3.00
	TrafficP = 1.00;// add 10&#37; for traffic
	pricepMile = 1.10;}// PPM &#163;1.00

 	if (distance <= 175); // less than 150 Mile
	{firstMile = 3.00; // FM &#163;3.00
	TrafficP = 1.00;// add 10% for traffic
	pricepMile = 1.15;}// PPM &#163;1.10
	
	if (distance <= 100); // less than 100 Mile
	{firstMile = 3.00; // FM &#163;3.00
	TrafficP = 1.00;// add 10% for traffic
	pricepMile = 1.20;}// PPM &#163;1.20
	
	if (distance <= 50); // less than 50 Mile
	{firstMile = 3.00; // FM &#163;3.00
	TrafficP = 1.00;// add 10% for traffic
	pricepMile = 1.30;}// PPM &#163;1.30
	
	if (distance <= 30); //less than 30 Mile
	{firstMile = 3.00; // FM &#163;2.50
	TrafficP = 1.00;// add 15% for traffic
	pricepMile = 1.40};// PPM &#163;1.40

	if (distance <= 15); // less than 15 Mile
	{firstMile = 2.20; // FM &#163;2.20
	TrafficP = 1.00;// add 00% for traffic
	pricepMile = 1.80};// PPM &#163;1.80 - standard tariff

[penagate]

Your sequence is backwards. If you are checking less-than conditions you need to start with the lowest number first, otherwise you end up executing every block.

I would try a different approach:

function calcFare(d)
{
	var tariffs = [
		{d: 15, fm:2.2, tm:1.00, ppm:1.80},
		{d: 30, fm:3.0, tm:1.15, ppm:1.40},
		{d: 50, fm:3.0, tm:1.10, ppm:1.30},
		{d:100, fm:3.0, tm:1.10, ppm:1.20},
		{d:175, fm:3.0, tm:1.10, ppm:1.15},
		{d:300, fm:3.0, tm:1.10, ppm:1.10}
	];

	for (var i in tariffs)
	{
		var T = tariffs[i];
		if (d <= T.d)
			return Math.max(2.2, (T.fm + (d - 1) * T.ppm) * T.tm);
	}

	return 2.2;
}

I assume that 2.20 is the minimum fare.
Also, you will need to change the actual tariff numbers. Mine are guesses based on your previous code snippets and comments, all of which seem to be in disagreement.

Also also... you don't have a condition for a distance greater than 300 miles.

[chris1990]

Thanks for your help penagate, i used a modified version of your code and got it working as i wanted.

The note you made about my sequence being backwards doesn't seem to be the case, using your code it ran the 300 line last, meaning the ppm is always 1.10 for anything under 300 miles. Where as backwards it runs the 15 line last which makes it work fine.

thanks, chris1990

[penagate]

The note you made about my sequence being backwards doesn't seem to be the case, using your code it ran the 300 line last, meaning the ppm is always 1.10 for anything under 300 miles. Where as backwards it runs the 15 line last which makes it work fine.

I think one of us is still confused...

Let's step through my code for a distance (d) of 20mi.
For the first tariff checked, T.d is 15 and so d<=T.d is not true.
For the next tariff checked, T.d is 30 and so d<=T.d is true and the function exits.

I don't see how you how got "ppm is always 1.10 for anything under 300 miles" from this.

I suppose as long as you've got it working, it doesn't matter.