Adding sum in a for loop in javascript

Question

I'm trying to recreate a simple project I have in my fundamentals class to javascript (from C++) but sum doesn't add every time the for loop runs. All other parts are ok but sum just lists the numbers in the order I put them in. Any help is appreciated

var num = prompt("Please enter an integer");
var lrg = num;
var sml = num;
var avg = num;
var sum = num;
var cnt = 10;

function runMath () {

for (i = 1; i < 10; i++) {
    var num = prompt("Please enter an integer");

    if (num > lrg) {
        lrg = num;
    } else {
        lrg = lrg;
    }

    if (num < sml) {
        sml = num;
    } else {
        sml = sml;
    }

    sum += num;

}
}

runMath();

avg = sum/cnt;

prompt returns a string.

Teemu
– Teemu

2015-05-28 18:26:43 +00:00
Commented May 28, 2015 at 18:26 — Teemu
– Teemu, Commented May 28, 2015 at 18:26
Use parseInt() on the return value of prompt.

user3745735
– user3745735

2015-05-28 18:27:43 +00:00
Commented May 28, 2015 at 18:27 — user3745735
– user3745735, Commented May 28, 2015 at 18:27

Danny Delott · Accepted Answer · 2015-05-28 18:30:11Z

1

The problem is that prompt() returns a String, whereas you are expecting a number. You can turn this into a number in a few different ways:

parseInt("33") will return 33, instead of "33"

Likewise, shorthand would look like:

+prompt("33") will return 33, instead of "33"

answered May 28, 2015 at 18:30

Danny Delott

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2 Comments

Asa Gayle Over a year ago

Thank you very much! Still learning and won't make that mistake again

Danny Delott Over a year ago

You're welcome! If this worked for you, please mark my answer as the correct one :)

James Newton · Accepted Answer · 2015-05-28 18:55:21Z

0

All input is from the prompt() command is a string. You can convert it to an integer using parseInt(), but the user can enter something other than a number, so you will need to check if it isNaN() (is Not a Number), and deal with it differently if it is.

var num = prompt("Please enter an integer");
num = parseInt(num, 10)
if (isNaN(num)) {
  alert ("That's not a number")
  num = 0 // or do something else
}

Caution: typeof NaN will return "number", so you can't rely on that as a test (see NaN)

An explanation of the + in +prompt: Unary plus (+)

edited May 28, 2015 at 18:55

answered May 28, 2015 at 18:36

James Newton

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1 Comment

Asa Gayle Over a year ago

Thank you! I'll be sure to add that in

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