Only the operating system has controlling of byte zero NULL in the computer's RAM and so if a function ever returns null, aka zero, well, something must have gone wrong because that can't possibly belong to me that memory because by human convention zero is owned by the operating system; not by a program I wrote.

只用操作系统在内存中能够控制,字节0，并且如果一个函数返回，或者说0，好的，可能出错了,因为那可能是不属于我的内存,因为惯例上，0是由操作系统拥有的,而不是由我的程序拥有的。

哈佛公开课 - 计算机科学课程节选

Now that's changing the more years that pass the more of you have 64-bit computers and the more servers have many, many gigabytes of RAM and so you need actually 64-bits, but for now let's assume a common system whereby a pointer just by definition of the homework is 32 bits.

现在计算机也在改变，也有更多的人,使用64位的计算机，更多的服务器有很多，很多G的内存，那样你就需要64位的，现在我们假设通常的系统中,根据家庭作业所定义的，一个指针为32位。

哈佛公开课 - 计算机科学课程节选