LeetCode : Perfect Number

We define the Perfect Number is a positive integer that is equal to the sum of all its positive divisors except itself.

Now, given an integer n, write a function that returns true when it is a perfect number and false when it is not.
Example:
Input: 28
Output: True
Explanation: 28 = 1 + 2 + 4 + 7 + 14

class Solution {
public:
    bool checkPerfectNumber(int num) {
         if(num==1)
             return false;
          int sum = 1;
          for(int i=2;i*i<=num;++i){
             if(num%i==0)
              {
                  sum+=(i+num/i);
              }
              if(i*i==num)
                   sum-=i;
              if(sum>num)
                   return false;
          }
          return sum==num;
    }
};