Javascript Loop - Adding a var to the while condition?

Question

Basically I want to count and display the amount of months it would take to get to a certain point (savings balance) based on a contribution every month.

Here is what I have so far:

function howLong(initial,interest,goal,added){
    var initialDeposit = parseInt(initial);
    var interestInt = parseInt(interest);
    var targetSaving = parseInt(goal);
    var contribution = parseInt(added);
    var monthCount = 0;
    while(initialDeposit <= targetSaving){
        monthCount++;
        initialDeposit+contribution
    }
    alert(monthCount)
}

Here is my html form:

<form>
Initial Deposit:<br />
<input type="number" id="initial"><br /><br />
Interest:<br />
<input type="number" id="interest"><br /><br />
Target savings amount:<br />
<input type="number" id="goal"><br /><br />
Monthly Contribution:<br />
<input type="number" id="contribution"><br /><br />
<input type="button" value="How Long!?" onclick="howLong(document.getElementById('initial').value,document.getElementById('interest').value,document.getElementById('goal').value),document.getElementById('contribution').value">
</form>

initialDeposit += contribution or initialDeposit = initialDeposit + contribution — vgru
– vgru, Commented Nov 23, 2018 at 12:13

Nina Scholz · Accepted Answer · 2018-11-23 12:33:03Z

1

You need to add the value of contribution to initialDeposit.

initialDeposit += contribution;

For the other problem, you have an error in the call of the function

document.getElementById('goal').value),document.getElementById('contribution').value"
                                     ^ >>>>>>>>>>>>>>>> should go >>>>>>>>>>>>>>>>> ^

shold be

onclick="howLong(
    document.getElementById('initial').value,
    document.getElementById('interest').value,
    document.getElementById('goal').value,
    document.getElementById('contribution').value
)"

The last round bracket is closing to early.

function howLong(initial, interest, goal, added) {
  var initialDeposit = parseInt(initial);
  var interestInt = parseInt(interest);
  var targetSaving = parseInt(goal);
  var contribution = parseInt(added);
  var monthCount = 0;
  while (initialDeposit <= targetSaving) {
    monthCount++;
    initialDeposit += contribution;
  }
  alert(monthCount)
}

<form>
  Initial Deposit:<br />
  <input type="number" id="initial"><br /><br /> Interest:
  <br />
  <input type="number" id="interest"><br /><br /> Target savings amount:<br />
  <input type="number" id="goal"><br /><br /> Monthly Contribution:<br />
  <input type="number" id="contribution"><br /><br />
  <input type="button" value="How Long!?" onclick="howLong(document.getElementById('initial').value,document.getElementById('interest').value,document.getElementById('goal').value,document.getElementById('contribution').value)">
</form>

edited Nov 23, 2018 at 12:33

answered Nov 23, 2018 at 12:14

Nina Scholz

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5 Comments

Kyle Over a year ago

It must be a problem in my form, this just gives me monthCount = 1 and shows it in an alert (using values initialDeposit = 1000, targetSaving = 1500, contribution = 50).

vgru Over a year ago

@Kyle: it says 11 here: jsfiddle.net/jgf0xh7o. If you get rid of the loop (like this, you will get 10, which is actually the correct answer (you should have < in your condition, not <=).

Kyle Over a year ago

@Groo Oh i see, so it's definitely my form then I guess?

Nina Scholz Over a year ago

right. it is the function, which have the closing bracket to early and omit the added parameter.

vgru Over a year ago

@Kyle: just note that <= is wrong, and you don't need a loop at all.

Rafael de Freitas · Accepted Answer · 2018-11-23 12:14:21Z

0

Change to initialDeposit += contribution;

answered Nov 23, 2018 at 12:14

Rafael de Freitas

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Comments

vgru · Accepted Answer · 2018-11-23 12:18:32Z

0

As other answers have pointed out initialDeposit += contribution will solve the issue, but you don't need a loop here at all:

var monthCount = Math.ceil((targetSaving - initialDeposit)/contribution);

This is presuming that the contribution is constant, of course.

answered Nov 23, 2018 at 12:18

vgru

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Comments

Prasad Telkikar · Accepted Answer · 2018-11-23 13:00:30Z

You were missing += operator and interest as well.

function howLong(){
    var initialDeposit = parseInt(document.getElementById('initial').value);
    var interestInt = parseInt(document.getElementById('interest').value);
    var targetSaving = parseInt(document.getElementById('goal').value);
    var contribution = parseInt(document.getElementById('contribution').value);
    var monthCount = 0;
    while(initialDeposit <= targetSaving){
        monthCount++;
        initialDeposit += contribution + interestInt; //+= was missing and interestInt as well
    }
    alert(monthCount);
}

<form>
Initial Deposit:<br />
<input type="number" id="initial"><br /><br />
Interest:<br />
<input type="number" id="interest"><br /><br />
Target savings amount:<br />
<input type="number" id="goal"><br /><br />
Monthly Contribution:<br />
<input type="number" id="contribution"><br /><br />
<input type="button" value="How Long!?" onclick="howLong()">
</form>

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