C编译器如何用二进制代码表示int数？

#include <iostream>

using std::cout;
using std::cin;
using std::endl;

int main()
{
    unsigned int a = 128;

    for (int i = sizeof(a) * 8; i >= 0; --i) {
        if (a & (1UL << i)) { // if i-th digit is 1
            cout << 1;        // Output 1
        }
        else {
            cout << 0;        // Otherwise output 0
        }
    }
    cout << endl;

    system("pause");

    return 0;
}

结果：

>对于a = 128：000000000000000000000000010000000,
>对于a = 127：100000000000000000000000002222211