【LeetCode】Multiply Strings

class Solution {
public:
    string multiply(string num1, string num2) {
        int m = num1.size();
        int n = num2.size();
        //record each digit of result in reverse order
        vector<int> result(m+n, 0); 
        //num index, the rightmost denotes as 0
        int ind1 = 0;   
        int ind2 = 0;

        for(int i = m-1; i >= 0; i --)
        {
            int carrier = 0;
            int n1 = num1[i]-‘0‘;
            //for every digit in num1, the num2 start with the rightmost digit
            ind2 = 0;   
            for(int j = n-1; j >= 0; j --)
            {
                int n2 = num2[j]-‘0‘;
                int product = n1*n2 + result[ind1+ind2] + carrier;
                carrier = product/10;
                result[ind1+ind2] = product%10;
                ind2 ++;
            }
            //all digits in num2 finished multiplication with num1[i]
            //the remaining carrier added in the right position
            result[ind1+ind2] += carrier;
            ind1 ++;
        }
        
        //skip 0s in the right of result
        while(result.size() > 0 && result[result.size()-1] == 0)
            result.pop_back();
        if(result.empty())
            return "0";
        else
        {
            string s;
            int i = result.size();
            while(i --)
                s += (‘0‘+result[i]);
            return s;
        }
    }
};