NB: If an argument to a function is a function pointer, you can write it like a normal function declaration.

So you can write

  void transform_string(char s[], char transform(char));

instead of having to write

  void transform_string(char s[], char(*transform)(char));

When writing C++ you should use function references when possible, as references cannot be null.

  void transform_string(char s[], char(&transform)(char));

Function references unfortunately require the more complex syntax, but fortunately C++11 `using`-style typedefs are quite simple to use with function types.

  using TransformFunc = char(char, char);
  typedef char TransformFunc(char, char); // C-style typedef, same as above

  // Function pointer
  TransformFunc fptr = /* ... */

  // Function reference
  TransformFunc &fref = /* ... */