Update src/expressions/operator-expr.md

Author: CAD97

src/expressions/operator-expr.md

@@ -404,6 +404,9 @@ Casting between pointers to unsized type preserves the pointer metadata unchange
 To illustrate:
 
 ```rust
+use std::ptr;
+
+```
 let u8_slice_ptr = ptr::slice_from_raw_parts::<u8>(ptr::null(), 4);
 assert_eq!((ptr::null(), 4), u8_slice_ptr.to_raw_parts());