Pretty straight forward. count numbers and put char.

1 class Solution { 2 public: 3     string getNext(string s) { 4         ostringstream oss; 5         char rec = s[0]; 6         int len = s.size(), num = 1; 7         for (int i = 1; i < len; i++) { 8             if (rec != s[i]) { 9                 oss << char(num + '0') << rec;10                 rec = s[i];11                 num = 1;12             } else num++;13         }14         oss << char(num + '0') << rec;15         return oss.str();16     }17     string countAndSay(int n) {18         string result = "1";19         for (int i = 2; i <= n; i++) {20             result = getNext(result);21         }22         return result;23     }24 };