https://leetcode.com/problems/add-strings/description/
class Solution {
public:
string addStrings(string num1, string num2) {
reverse(num1.begin(), num1.end());
reverse(num2.begin(), num2.end());
string ans;
int len1 = num1.length(), len2 = num2.length(), i = 0, flag = 0;
while (i<len1 || i<len2) {
int val = 0;
if(i<len1) val += (num1[i] - '0');
if(i<len2) val += (num2[i] - '0');
ans += (val+flag)%10 + '0';
flag = (val+flag)/10;
i++;
}
if(flag) ans += '1';
reverse(ans.begin(), ans.end());
return ans;
}
};