判断以下C++代码能否正确计算整数N和M之间所有整数之和（包含N和M）

int N, M, Sum;
cin >> N >> M;
if (N > M){
    int tmp = N;
    N = M, M = tmp;
}
for (int i = N; i < M+1; i++)
    Sum += i;
cout << Sum;