# #if directive

Source: https://ref.dm-lang.org/DM/preprocessor/if

### Format
- `#if Val`
- `...`
- `#elif Val2`
- `...`
- `#else`
- `...`
- `#endif`


### Args
> Val: A logical expression.

The `#if` statement is used to conditionally compile code. If Val is true (non-zero), the code following the `#if` statement will be compiled. Otherwise, compilation skips to the next `#elif`, `#else`, or `#endif` statement.

The function `defined()` can be used in the conditional expression. It is true if its argument is a defined macro (with `#define`) and false otherwise.

```dm
#if defined(DEBUG)
// This code will be compiled if DEBUG is
// defined
#else
// This code will be compiled if DEBUG is
// not defined
#endif
```

You can also use `fexists()` in a conditional to check if a file exists.

### See also
- [#define directive](https://ref.dm-lang.org/DM/preprocessor/define/index.md)
- [#ifdef directive](https://ref.dm-lang.org/DM/preprocessor/ifdef.md)