leetcode - Count and Say

class Solution {
public:
string genNext(string cur){
string rlt = "";
char t[20];
int length = cur.length();
int i = 0;
char c = cur.at(0);
int len = 0;
while(i<length){
while (i<length && cur.at(i)==c){
len++;
i++;
}
sprintf(t, "%d%c", len, c);
rlt += t;
len =0;
if (i<length){
c = cur.at(i);
}
}
return rlt;
}
string countAndSay(int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
string rlt = "1";
while (--n > 0){
rlt = genNext(rlt);
}
return rlt;
}
};