> **12.** Suppose that the macro `M` has been defined as follows:
```c
#define M 10
```
> Which of the following tests will fail?
// C will fail, because `M` is defined.
#ifndef M
---
> **13.** Show what the following program will look like after preprocessing. You may ignore any lines added to the program as a result of including the `<stdio.h>` header.
