//1
#include<bits/stdc++.h>
using ll = long long ;
using ull = unsigned ll ;
signed main ( ) {
    ull x = 0 ; x ++ ; std::cout << (int)x << '\n';
    
}

//2
#include<bits/stdc++.h>
using ll = long long ;
using ull = unsigned ll ;
signed main ( ) {
    ull x = 0 ; x ++ ; std::cout << x << '\n';
    
}
//3
#include<bits/stdc++.h>
using ll = long long ;
using ull = unsigned long long ;
signed main ( ) {
    ull x = 0 ; x ++ ; std::cout << x << '\n';
    
}

为什么代码 2 CE 了而 1 和 3 都没有 CE 啊？

很不理解。