LeetCode-Count and Say

The count-and-say sequence is the sequence of integers beginning as follows:

1, 11, 21, 1211, 111221, ...

1

 is read off as 

"one
1"

 or 

11

.

11

 is read off as 

"two
1s"

 or 

21

.

21

 is read off as 

"one
2

, then 

one 1"

 or 

1211

.

Given an integer n, generate the nth sequence.

Note: The sequence of integers will be represented as a string.
Solution:
Code:

class Solution {
public:
string countAndSay(int n) {
if (n == 0) return "";
if (n == 1) return "1";
string str = "1";
while (n > 1) {
string temp;
--n;
int length = str.size();
for (int i = 0; i < length;) {
char c = str[i];
int count = 0;
while (i < length && str[i] == c) {
++i;
++count;
}
temp += to_string(count)+c;
}
str = temp;
}
return str;
}
};