Improve code in example/

[gruenich]

Fix warnings.
Make variables more local, e.g., just inside for loops.
Add missing headers.
Add return statements for int main(..)

[xiaoyeli]

Why is is the following better?
"Make variables more local, e.g., just inside for loops."

[gruenich]

Why is is the following better?
"Make variables more local, e.g., just inside for loops."

I am glad you ask this question!

1. In the past the advice was different. Pascal, Ada, C (from 1989) all forced to declare variables at the very beginning. This has changed in Java, Python and C (since 1999) to have localized variables as much as possible.
2. It prevents silly mistakes likes mixing up j with i, as only the right variable is defined and the compiler will complain.
3. It is easier to read, as the variable declaration (and the type of the variable) is close to its use.

Two sources to support my claim with different arguments:

• https://wiki.sei.cmu.edu/confluence/display/c/DCL19-C.+Minimize+the+scope+of+variables+and+functions
• https://www.oreilly.com/library/view/c-coding-standards/0321113586/ch19.html

[xiaoyeli]

ok, declaring variable inside the loop was considered bad in the old style. But now as long as the compiler knows not to repeatedly generate new variables, it would be fine.