Problem
1. Must all of the keys of an array be of the same type?
2. What exactly do the array_keys and array_values functions do?
3. What exactly does the in_array function do?
4. Explain the actions of the implode and explode functions.
5. Describe the actions of the next, reset, and prev functions.
6. What are the syntax and semantics of the two forms of the foreach statement?