CODEWITHSUNDEEP
javascript
Antonio Pavicevac-Ortiz
Antonio Pavicevac-Ortiz

Reputation: 7729

Why does this function return NAN

If I use <= instead of <, I'll get NaN, why?

function addArgs(){
    var sum = 0, count = 0;

    while(count <= arguments.length){

         sum += arguments[count];
         count++;
    }
    return sum;
}

Upvotes: 0

Views: 149

Answers (5)

Sherali Turdiyev
Sherali Turdiyev

Reputation: 1743

All iterations start from 0(Also, count = 0 in your code). So, max count equals arguments.length-1.

addArgs(2,5,8); -> arguments[0] = 2; arguments[1] = 5; arguments[2] = 8;

Besides that, you can use <= when count starts from 1

function addArgs(){
    var sum = 0, count = 1;

    while(count <= arguments.length){

         sum += arguments[count-1];
         count++;
    }
    return sum;
}
addArgs(2,3,4);//9

Upvotes: 1

Iliiaz Akhmedov
Iliiaz Akhmedov

Reputation: 877

Suppose your argument is 3 elements:

arguments = [0, 1, 2]

Your count will iterate as 0 => 1 => 2 => 3 (and on 3rd you are out of bound of the array, since it has 3 elements, but indexed starting with 0.

That's basics of iterating through loop.

Upvotes: 3

Racil Hilan
Racil Hilan

Reputation: 25341

When you iterate through a list and use the index to access the items of the list (like you're doing), you always iterate up to length - 1 or < length. The reason is that the list index starts from zero, not one. For instance, a list of 3 items has it's length equals 3 and the indexes of its items are 0, 1, and 2. There is no item with index 3, so if you iterate up to length or <= length, the counter will reach 3 in the last iteration and the attempt to retrieve the item with the index 3 will fail and return undefined.

Finally, adding the undefined to the sum will results in a NaN because undefined is not a number.

Upvotes: 2

gefei
gefei

Reputation: 19766

in the last iteration of your loop, count is arguments.length, therefore arguments[count] === arguments[arguments.length] === undefined, and sum += undefined results in sum === NaN

Upvotes: 3

CiceroDev
CiceroDev

Reputation: 31

It seems that arguments[count] is not a number (NaN). In Javascript, when the second argument in an expression is not a number, the first one is also treated as not a number.

Thus, sum ends up the function being treated as another data type.

http://www.w3schools.com/js/js_datatypes.asp

Upvotes: 2

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