Values have a type and a binary representation.
The binary representation of a type is a model that describes the possible values for that type. It is not the same as the in-memory object representation that describes the more or less physical storage of values of a given type.
TAKEAWAY 5.49
TAKEAWAY 5.49 The same value may have different binary representations.
All basic C types are kinds of numbers, but not all of them can be used directly for arithmetic.
C programs run in an abstract state machine that is mostly independent of the specific computer where it is launched.
在 C 语言刚刚被设计出来的时候，一共只有两种整数类型 —— char 和 int。C89 引入了两种新的整数类型 —— short 和 long，C99 再增加一种整数类型 —— long long。
后来，随着 C 语言的进一步发展，K&R C 引入了无符号整数的概念以及 unsigned 关键字。char 既不属于标准带符号整数类型也不属于标准无符号整数类型，它属于历史遗物。
C89 引入 signed 关键字后，可显式声明 signed char，明确表达最小的标准带符号整数类型。
为什么 getchar() 返回的类型是 int，而不是 char？