## identifier 标识符ID | Unique
Identifier refers to name given to entities such as
`variables`, `functions`, `structures` etc.
## type qualifier 类型限制
In the C, C++, and D programming languages, a type qualifier is a `keyword` that is applied to a type, resulting in a qualified type.
For example, `const int` is a qualified type representing a constant integer, while int is the corresponding `unqualified type`, simply an integer.
In D these are known as `type constructors`, by analogy with constructors in object-oriented programming.
As of 2014 and C11, there are four type qualifiers in standard C:
`const` (C89), `volatile` (C89), `restrict` (C99) and `_Atomic` (C11)
## Runtime && Compile time | 编译型语言特点~ like `C`
### Refer
[StackOverflow](https://stackoverflow.com/questions/846103/runtime-vs-compile-time)
### Compile time 错误判断
* 语法 | Syntax errors
* 拼写 | Typechecking errors
* 崩溃 | (Rarely) compiler crashes
### Runtime 错误判断
* 零除 | Division by zero
* 错误引用 | Dereferencing a null pointer
* 内存边界 | Running out of memory