题目链接
大数求和

   class Solution {
    public:
        string addStrings(string num1, string num2) {
            int cf = 0;//进位
            int temp;
            string str;
            int n;
            int len_num1 = num1.size();
            int len_num2 = num2.size();
            int len = abs(len_num1 - len_num2);
            //长度对齐
            if(len_num1 < len_num2)
            {
                for(int i=0;i<len;i++)
                {
                    num1 = "0"+num1;
                }
            }
            else
            {
                for(int i=0;i<len;i++)
                {
                    num2 = "0"+num2;
                }
            }
            len_num1 = num1.size();
            //字符串相加
            for(int i=len_num1-1;i>=0;i--)
            {
                n = num1[i] - '0'+ num2[i] - '0' + cf;
                cf = n/10;
                temp = n%10;
                str = to_string(temp) + str;
            }
            if(cf != 0)
                str = to_string(cf)+str;
            return str;
        }
        };