Sum of given number

General Algorithm for sum of digits in a given number:

  • Get the number
  • Declare a variable to store the sum and set it to 0
  • Repeat the next two steps till the number is not 0
  • Get the rightmost digit of the number with help of the remainder ‘%’ operator by dividing it by 10 and add it to sum.
  • Divide the number by 10 with help of ‘/’ operator to remove the rightmost digit.
  • return the sum

Solution-1 

function sumOfDigits(n) {
    let sum = 0;
    
    while(n < 0) {

        // get the last digit
        sum = sum + n % 10;

        // divide the number by 10 we get float
        // parse the number to int to remove last digit
        n = parseInt(n / 10);
    }

    return sum;
}

console.log(sumOfDigits(123));

Solution-2: 

function sumOfDigits(n) {
    let sum;
 
    for(sum = 0; n > 0;
        sum += n % 10,
        n = parseInt(n / 10));

    return sum;
}

console.log(sumOfDigits(123));

Solution-3: 

function sumOfDigits(n) {
    return n == 0 ? 0 : n % 10 + sumOfDigits(parseInt(n/10));
}

console.log(sumOfDigits(123));
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