Invalid C ++ Merge

I am trying to implement a merge sort, but I cannot get it to work. I would be very grateful if anyone could find and point out an error in my thinking (and code). The main function without unnecessary code:

int main(int argc, char *argv[]) {
    int n = 0;
    std::cin >> n;
    int num[n];

    for(int i = 0; i < n; i++) {
        std::cin >> num[i];
    }

    sort(num, &num[n - 1], n);

    return(0);
}

Merge Sort Function:

int *sort(int *s, int *e, int size) {
    if(s == e) {
        return(s);
    }

    int mid = (size + 1) / 2;

    //split array recursively to 1-element arrays

    int *left  = sort(s, (s + mid - 1), mid);
    int *right = sort(s + mid, e, size - mid);

    int *counter = s;

    //merge arrays back together

    while(left < (s + mid - 1) && right <= e) {
        //std::cout << *left << " " << *right << std::endl;

        for(; left < (s + mid - 1) && *left <= *right; left++, counter++) {
            *counter = *left;
        }

        for(; right <= e && *right <= *left; right++, counter++) {
            *counter = *right;
        }
    }

    for(; left < (s + mid - 1); left++, counter++) {
        *counter = *left;
    }
    for(; right <= e; right++, counter++) {
        *counter = *right;
    }

    return(s);
}

input0:
5
4 3 2 1 0
output0:
0 0 0 0 0

input1:
5
0 1 2 3 4
output1:
1 2 4 4 4

input2:
2
0 1
output2:
1 1