beause there is no 'zero' ,so we should make the 'Z'(26) corresponding to 'zero',so if the mod is zero,it means 'Z' and meanwhile n=n/26-1

```
class Solution {
public:
string convertToTitle(int n) {
string ans;
while (n>0)
{
if (n%26==0)
{
ans='Z'+ans;
n=n/26-1;
}
else
{
ans=(char)('A'+n%26-1)+ans;
n=n/26;
}
}
return ans;
}
};
```