258. Add Digits

本来想看看这样行不行，结果一下就AC了，超开心

可能这道题就是十位和个位吧

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

For example:

Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return it.

int addDigits(int num) { while(num/10!=0){ int a=0,b=0; a=num; b=(num-num)/10; num=a+b; } return num; }