Develop Reference

How can I display addition operation? [duplicate]

I am creating an seat booking page with html/javascript.
This is part of the criteria I am working on:
When Passengers 1 to 4, Add £0.10 to Fare per mile
When number of miles is less than or equal to 10, then Fare per mile is £1.-
The problem is, is that when I try to add together the total cost + cost for passengers, it concatenates the variable (tried it both ways).
Any help would be greatly appreciated.
function MyFunction() {
var x, text, passengers, passengerresponse, cost;
miles = document.getElementById("miles").value;
if (isNaN(miles) || miles < 1) {
text = "Input not valid";
} else if (miles <= 10) {
cost = miles;
}
document.getElementById("miles2").innerHTML = miles;
passengers = document.getElementById("passengers").value;
if (passengers >= 1 && passengers <= 4) {
passengerresponse = "OK";
cost += passengers / 10;
}
document.getElementById("passengers2").innerHTML = passengers;
document.getElementById("totalcost").innerHTML = cost;
}
Journey in miles:
<input id="miles" type="number">
<p id="miles2"></p>
Number of passengers:
<input id="passengers" type="number">
<p id="passengers2"></p>
<button type="button" onclick="MyFunction()">Submit</button>
Total cost:
<p id="totalcost"></p>

passengers is a string, not a number. You're doing the same thing as saying cost = 'Santa' + 'Claus'; The fact that it's cost = '1' + '4'; doesn't change the '1' and '4' to a 1 and 4.
The solution is to use parseInt, Number, or one of the method from this answer.

You should convert passengers to numerical value.
Method 1 + unary oprerator
passengers = +document.getElementById("passengers").value;
Method 2 parseInt()
passengers = +document.getElementById("passengers").value;
passengers = parseInt(passengers, 10);

Cost is undefined if you put any miles in greater than 10. When you add undefined to the number of passengers, the result is Not a Number (NaN).
Also, I would recommend you use parseInt on the data you're retrieving from the inputs. Right now you're pulling them in as strings and doing math on them, which only works because Javascript has been smart enough to implicitly cast them as numeric where necessary.
function MyFunction()
{
var x, text, passengers, passengerresponse, cost;
miles = document.getElementById("miles").value; // miles is a string
miles = parseInt(miles, 10); // convert to numeric base 10
if (isNaN(miles) || miles < 1)
{
text = "Input not valid";
}
else if (miles <= 10)
{
cost = miles;
}
// if miles > 10, cost is undefined
if(!cost) cost = 0;
document.getElementById("miles2").innerHTML = miles;
passengers = document.getElementById("passengers").value; // passengers is a string
passengers = parseInt(passengers, 10); // convert passengers to a number
if (passengers >= 1 && passengers <= 4 )
{
passengerresponse = "OK";
console.log(cost, passengers);
cost += passengers / 10;
}
document.getElementById("passengers2").innerHTML = passengers;
document.getElementById("totalcost").innerHTML = cost;
}

Application that calculates price depending on quantity in JavaScript

I have this exercise that I am struggling to comprehend the logic to achieve the outcome when qty is more than 3:
An application to calculate the price of pizzas (listed below) that will be purchased during a promotional period. The number of pizzas will be entered by the user.
One large pizza will cost $6.45.
Two large pizzas will cost $12.00.
Three large pizzas will cost $14.00.
Four or more pizzas will use a combination of the above prices to ensure the best price for the customer. For example, the best price for five pizzas would be two pizzas ($12.00) + three pizzas ($14.00).
The algorithm must also take account of all possible situations by using sequence, selection and iteration structures.
Below is my code so far:
let calcOrder = () => {
// get inputs
var qty = document.getElementById("quantity").value;
var price = 6.45;
var price2 = 12.0;
var price3 = 14.0;
var totalPrice;
// validate missing, non-digit, negative inputs
if (qty == "") {
document.getElementById("message").innerHTML = "Missing input";
} else if (isNaN(qty)) {
document.getElementById("message").innerHTML = "Numbers only";
} else if (qty < 0) {
document.getElementById("message").innerHTML =
"Negative numbers are not allowed";
} else {
//calc total
if (qty == 1)
{
totalPrice = price;
}
else if (qty == 2)
{
totalPrice = price2;
}
else if (qty == 3)
{
totalPrice = price3;
}
//output total
document.getElementById("message").innerHTML =
`Total price is $${totalPrice}`;
}
// prevent form from submission
return false;
};
Thank you

you can use division and mod operation to calculate the price:
(this example assuming all check you did valid input are already done)
const qte = document.getElementById("quantity").value;
const price = 6.45;
const price2 = 12.0;
const price3 = 14.0;
let totalPrice;
const total3 = parseInt("" + qte / 3 + "", 10) * price3;
const total2 = parseInt("" + (qte % 3) / 2 + "", 10) * price2;
const total1 = parseInt("" + ((qte % 3) % 2) + "", 10) * price;
totalPrice = total1 + total2 + total3;
document.getElementById("message").innerHTML =
`Total price is $${totalPrice}`;
what is actually happening in the code
well it is basic mathematics, if you want to know how many 3s in your number you divide by 3 and take the integer part or floor of the result, basic division. for example 10 = 3*3 + 1 so you have 3 as a result of that division.
since you only want to apply the price of 3 pizza as top priority you do this division then multiply by the price for 3.
then come the priority for the price of 2 pizzas, but you not interested for the total number of pizzas, only what was left after you payed with the price of 3 pizzas so you do the mod operator (%) with 3 to get was left unpaid, for example 8 = 3*2 + 2, this give us 2 pizzas left unpaid so you apply the price of 2 pizzas.
the you check if a single pizza is left after you paid for 2 pizzas (which would only happen if only a single pizza was left after you paid for 3). if there is single pizza you pay for it otherwise you add nothing.
ps: after paying for pizzas in multiple of three, you only add the price of 2 pizzas or a single one, but never both, otherwise price of 3 pizzas would apply instead.
hope the explanation is clear, if not leave a comment and i'll try to adjust what was not clear.

Can I force percentages to sum up to a exact value?

I have a fixed tax value, say USD 50,00, and I want to divide this tax among people. So, one person can select how much of the tax he will pay. Once this person selects its quota, the remaining of the tax is divided among the others.
I have made a javascript(I am using EmberJs) function to do this automatically but sometimes the value is evaluated to more than USD 50 and sometimes less.
My function:
percentageFromValue(person, selectedValue){
selectedValue = selectedValue.replace(/[R$\s]/g,'');
selectedValue = selectedValue.replace(/[,]/g,'.');
selectedValue = parseFloat(selectedValue);
let taxValue= this.get('taxValue');
///nao deixar valor utrapasse o valor da taxa
if(selectedValue> taxValue)
valor = taxValue;
let personPercentage = (selectedValue*100.0 / taxValue);
personPercentage = parseFloat(personPercentage );
let parcialSum= 0;
person.set('pctTax',personPercentage.toFixed(2));
let remainingPercent= 100.0 - personPercentage ;
let totalPersons = this.get('persons.length');
let pctPerPerson= remainingPercent/ (totalPersons - 1);
let valuePerPerson= (pctPerPerson* taxValue) / 100.0;
this.get('persons').forEach(r =>{
if(person.get('id') != r.get('id')){
r.set('pctTax',pctPerPerson);
r.set('value',valuePerPerson.toFixed(2));
}
});
},
How Can I make this automatic redistributions to always sum up to USD 50,00??

This is more of a rounding problem than a programming problem.
Say you want to divide a $50 tax among three people... 50/3 = 16.6666666... assuming it's a currency and you round up to two decimals, each person pays $16.66 and the sum is 16.66 * 3 = 49.98.
If there is no requirement of having all people paying the exact same amount of tax every time, I'd just add/subtract the rounding difference from the first person:
let remainingPercent= 100.0 - personPercentage ;
let totalPersons = this.get('persons.length');
let pctPerPerson= remainingPercent/ (totalPersons - 1);
let valuePerPerson= (pctPerPerson* taxValue) / 100.0;
let roundingError = taxValue - pctPerPerson * totalPersons;
this.get('persons').forEach(r =>{
if(person.get('id') != r.get('id')){
r.set('pctTax',pctPerPerson);
if (this.indexOf(r) == 0) {
r.set('value',valuePerPerson.toFixed(2) + roundingError);
} else {
r.set('value',valuePerPerson.toFixed(2));
}
}
});

Javascript variables not adding two variables correctly, only concatenating

I am creating an seat booking page with html/javascript.
This is part of the criteria I am working on:
When Passengers 1 to 4, Add £0.10 to Fare per mile
When number of miles is less than or equal to 10, then Fare per mile is £1.-
The problem is, is that when I try to add together the total cost + cost for passengers, it concatenates the variable (tried it both ways).
Any help would be greatly appreciated.
function MyFunction() {
var x, text, passengers, passengerresponse, cost;
miles = document.getElementById("miles").value;
if (isNaN(miles) || miles < 1) {
text = "Input not valid";
} else if (miles <= 10) {
cost = miles;
}
document.getElementById("miles2").innerHTML = miles;
passengers = document.getElementById("passengers").value;
if (passengers >= 1 && passengers <= 4) {
passengerresponse = "OK";
cost += passengers / 10;
}
document.getElementById("passengers2").innerHTML = passengers;
document.getElementById("totalcost").innerHTML = cost;
}
Journey in miles:
<input id="miles" type="number">
<p id="miles2"></p>
Number of passengers:
<input id="passengers" type="number">
<p id="passengers2"></p>
<button type="button" onclick="MyFunction()">Submit</button>
Total cost:
<p id="totalcost"></p>

passengers is a string, not a number. You're doing the same thing as saying cost = 'Santa' + 'Claus'; The fact that it's cost = '1' + '4'; doesn't change the '1' and '4' to a 1 and 4.
The solution is to use parseInt, Number, or one of the method from this answer.

You should convert passengers to numerical value.
Method 1 + unary oprerator
passengers = +document.getElementById("passengers").value;
Method 2 parseInt()
passengers = +document.getElementById("passengers").value;
passengers = parseInt(passengers, 10);

Cost is undefined if you put any miles in greater than 10. When you add undefined to the number of passengers, the result is Not a Number (NaN).
Also, I would recommend you use parseInt on the data you're retrieving from the inputs. Right now you're pulling them in as strings and doing math on them, which only works because Javascript has been smart enough to implicitly cast them as numeric where necessary.
function MyFunction()
{
var x, text, passengers, passengerresponse, cost;
miles = document.getElementById("miles").value; // miles is a string
miles = parseInt(miles, 10); // convert to numeric base 10
if (isNaN(miles) || miles < 1)
{
text = "Input not valid";
}
else if (miles <= 10)
{
cost = miles;
}
// if miles > 10, cost is undefined
if(!cost) cost = 0;
document.getElementById("miles2").innerHTML = miles;
passengers = document.getElementById("passengers").value; // passengers is a string
passengers = parseInt(passengers, 10); // convert passengers to a number
if (passengers >= 1 && passengers <= 4 )
{
passengerresponse = "OK";
console.log(cost, passengers);
cost += passengers / 10;
}
document.getElementById("passengers2").innerHTML = passengers;
document.getElementById("totalcost").innerHTML = cost;
}

Plus equals operator error

Hello so I'm trying to get the += to increase value of balance. I now understand that in java script use += is to pass by reference, but how can I use it to pass by value.
alert("Welcome to the Online Bank Teller");
var balance = 100.00;
var amount;
var run = true;
do{
var pick = prompt("Make a selection...\n1-Check Balance, 2-Deposit, 3-Withdraw, 4-Quit");
if(pick == 1){alert("Your balance is: $" + balance.toFixed(2));}
else if(pick == 2){
amount = prompt("Enter the amount you want to deposit: $");
if(amount > 1000){alert("You can only enter up to $1000 per deposit!");}
Right here--->balance += amount;
alert("Your new balance: $" + balance.toFixed(2));
}
else if(pick == 3){
amount = prompt("Enter the amount you want to withdraw: $");
if(amount > balance){alert("Amount exceeded account balance!");}
else if(amount > 500){alert("The max you can take out is up to $500 per withdraw!");}
else if (amount <= balance){
balance -= amount;
alert("Your new balance: $" + balance.toFixed(2));
}
}
else if(pick == 4){run = false;}
else{alert("Not a valid choice!");}
}while(run)
How can I get it to alter the value inside of the variable when the user enters a new deposit.
I get
Your balance is: $10022
instead of
Your balance is: $122
Thanks in advance...

use parseInt() function to each amount which is getting from prompt
amount = parseInt(prompt("Enter the amount you want to deposit: $"), 10);
DEMO

Try
balance = parseInt(balance) += parseInt(amount);
Balance and amount are strings, so for example:
Adding the string '50' to the string of '3' woul make '503'
Adding the float value of '50' to the float value of '3' would make '53'

As an alternative to the parseInt function that has already been mentioned, there are some "quick&dirty" ways to do it:
amount = 1 * prompt("Enter the amount you want to deposit: $");
// get'S converted because * is only defined on numbers
amount = +prompt("Enter the amount you want to deposit: $");
// converted because unary + is only defined on numbers
and a couple of other, less common ones.

Adding a string to a number with += operator produces a string.
prompt() returns a string, hence you need to convert the return values to a number:
balance += +amount;
Or use parseFloat() to convert values. Though I can't understand how you'd get anything alerted, since strings haven't toFixed() method, and hence the alert() in your code is supposed to trigger an error.