C++ 无符号整型和整型的区别

#include<iostream>
#define ZERO 0
using namespace std;
#include<climits>
int main()
{   
    short nu1 = SHRT_MAX;
    unsigned short nu2 = nu1;
    cout << "nu1 has " << nu1 << " and nu2 has " << nu2 << endl;
    cout << "如果每个数都加一呢？" << endl;
    nu1 = nu1 + 1;
    nu2 = nu2 + 1;
    cout << "Now nu1 has " << nu1 << " and nu2 has " << nu2 << endl<<endl;
    nu1 = ZERO;
    nu2 = ZERO;
    cout << "nu1 has " << nu1 << " and nu2 has " << nu2 << endl;
    cout << "如果每个数减一呢？" << endl;
    nu1 = nu1 - 1;
    nu2 = nu2 - 1;
    cout << "Now nu1 has " << nu1 << " and nu2 has " << nu2 << endl;
    cin.get();
    return 0;
}