LeetCode - Single Number

Given an array of integers, every element appears twice except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

class Solution {
public:
    int singleNumber(int A[], int n) {
        int num=0;
        if(n<=0){
            return num;
        }
        num=A[0];
        for(int i=1;i<n;i++){
            num^=A[i];
        }
        return num;
    }
};