Return sum of a number (positive or negative)

问题:

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 ?

回答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));

回答2:

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));