Assn03 Ques07 Missing Number

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int size = nums.size();
        for (int checkNum = 0; checkNum <= size; checkNum++) {
            bool present = false;
            for (int j = 0; j < size; j++){
                if (nums[j] == checkNum){
                    present = true;
                }
            }
            if (present == false){
                return checkNum;
            }
        }
        return -1;
    }
};