Sfida di programmazione: Sum of Digits

Problema

Add up every decimal digit of n. For 352 the digits are 3, 5 and 2.

Implement sum_of_digits(n).

n: A positive integer.

Return the sum of its digits.

1 ≤ n ≤ 10¹⁸

Esempio 1

Input:
n = 352

Output atteso:
expected = 10

Input:
long long n = 352;

Output atteso:
long long expected = 10;

Input:
long n = 352;

Output atteso:
long expected = 10;

3 + 5 + 2 = 10.

Esempio 2

Input:
n = 1000

Output atteso:
expected = 1

Input:
long long n = 1000;

Output atteso:
long long expected = 1;

Input:
long n = 1000;

Output atteso:
long expected = 1;

1 + 0 + 0 + 0 = 1.