I need to make a function that takes a number and returns sum of it's digits, if the number is negative the first digit should be considered negative when adding numbers, this is what I have:

var arrx = [];
var oper;
var others = 0;

function sumDigits(num) {
    // your code here
    var y = num.toString();
    var c = y.split("");
    c.forEach((h) => arrx.push(Number(h)) );
    if (num < 0){
        oper = -arrx[0];
        for (var z = 1; z < arrx.length; z++){
            others += arrx[z];
        }

        return others + oper;
    }

    return arrx.reduce((a,b) => a+b);
}

sumDigits(1234);

When given negative number, function returns NaN, what's the problem ?

I need to make a function that takes a number and returns sum of it's digits, if the number is negative the first digit should be considered negative when adding numbers, this is what I have:

var arrx = [];
var oper;
var others = 0;

function sumDigits(num) {
    // your code here
    var y = num.toString();
    var c = y.split("");
    c.forEach((h) => arrx.push(Number(h)) );
    if (num < 0){
        oper = -arrx[0];
        for (var z = 1; z < arrx.length; z++){
            others += arrx[z];
        }

        return others + oper;
    }

    return arrx.reduce((a,b) => a+b);
}

sumDigits(1234);

When given negative number, function returns NaN, what's the problem ?

• javascript
• arrays
• sum
• digits

Share Improve this question Follow edited Apr 12, 2018 at 1:40 Cœur 38.8k2525 gold badges206206 silver badges279279 bronze badges asked Jan 29, 2017 at 22:38 user7451361user7451361 2

• Why do you push the digits to an array when c is already one? – Code-Apprentice Commented Jan 29, 2017 at 23:03
• I suggest developing an algorithm that works directly with numbers rather than converting the number to a String. Can you think of a way to get the ones digit from a number? How do you get the rest of the number other than the ones digit? – Code-Apprentice Commented Jan 29, 2017 at 23:04

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2 Answers 2

Sorted by: Reset to default 1

Use optimized and short version of sumDigits() function:

function sumDigits(num) {
  var isNeg = num < 0,   // check whether the number is negative
      numbers = (isNeg? String(num).slice(1) : String(num)).split('').map(Number);
  if (isNeg) numbers[0] *= -1;   // 'recovering' the number's sign

  return numbers.reduce(function(a,b){ return a + b; });
}

console.log(sumDigits(1234));
console.log(sumDigits(-951));

In case of negative number, the first char is '-' the minus symbol. When you are trying to convert it to number, you are getting NaN. After that if you try to add NaN to any number the result would be NaN.

As a resolution, you need to ignore the first digit if the number is negative.

So, you can make a code change like

if(z === 1){
    others = others - arrx[z];
    }else{
     others += arrx[z];
      }

and also changing the return in case of negative numbers to return others;

Following code should work.

var arrx = [];
var oper;
var others = 0;

function sumDigits(num) {
 // your code here

var y = num.toString();

var c = y.split("");

c.forEach((h) => arrx.push(Number(h)) );

if (num < 0){


for (var z = 1; z < arrx.length; z++){

  if(z === 1){
    others = others - arrx[z];
    }else{
     others += arrx[z];
      }

}

return others;
}

return arrx.reduce((a,b) => a+b);

}
console.log(sumDigits(-1234));