减法运算中的整数溢出类型

我正在尝试再学习C++,使用SAMS自学C++ 21天(第六版)。我试着把它做得非常彻底,确保我理解每一章(尽管我已经熟悉C语法语言)。

在第5章(清单5.2)的开头,有一点是关于无符号整数溢出的。根据他们的例子,我写了如下:

#include <iostream>

int main () {
    unsigned int bignum = 100;
    unsigned int smallnum = 50;
    unsigned int udiff;
    int diff;
    udiff = bignum - smallnum;
    std::cout << "Difference (1) is " << udiff << "\n";
    udiff = smallnum - bignum;
    std::cout << "Difference (2) is " << udiff << "\n";
    diff = bignum - smallnum;
    std::cout << "Difference (3) is " << diff << "\n";
    diff = smallnum - bignum;
    std::cout << "Difference (4) is " << diff << "\n";
    return 0;
}

这给出了以下输出,这对我来说并不奇怪:

Difference (1) is 50
Difference (2) is 4294967246
Difference (3) is 50
Difference (4) is -50

如果我更改程序使 bignum 改为读取 unsigned int bignum = 3000000000; 然后输出是

Difference (1) is 2999999950
Difference (2) is 1294967346
Difference (3) is -1294967346
Difference (4) is 1294967346

第一个显然很好。 1294967346 是因为 1294967346个 正是 2^32 - 3000000000 . 我不明白为什么第二行不读 1294967396 ,由于 smallnum .

第三个 第四行 我无法解释。这些结果是如何产生的?

编辑:对于第三行-它仅仅通过找到解的模来给出这个结果吗 2^32