Editing Avionics software (section)

===Code production and review===
The code is written, then usually reviewed by a programmer (or group of programmers, usually independently) that did not write it originally (another legal requirement). Special organizations also usually conduct code reviews with a checklist of possible mistakes. When a new type of mistake is found it is added to the checklist, and fixed throughout the code.

The code is also often examined by special programs that analyze correctness ([[Static code analysis]]), such as SPARK examiner for the [[SPARK programming language|SPARK]] (a subset of the Ada programming language) or [[Lint programming tool|lint]] for the C-family of programming languages (primarily C, though).
The [[compiler]]s or special checking programs like "lint" check to see if types of data are compatible with the operations on them, also such tools are regularly used to enforce strict usage of valid programming language subsets and programming styles.
Another set of programs measure [[software metric]]s, to look for parts of the code that are likely to have mistakes.
All the problems are fixed, or at least understood and double-checked.

Some code, such as [[digital filter]]s, [[graphical user interface]]s and [[inertial navigation system]]s, are so well understood that software tools have been developed to write the software.  In these cases, specifications are developed and reliable software is produced automatically.