========
Pointers                                                                [TOC]
========

We start with some simple examples on pointers.  Recall:

- With `&i` we get the address of a variable `i`.  If `i` has type `int` then
  `&i` is of type `int *`.
- Assume `j` is a pointer to `int` (i.e. of type `int *`) then the content of
  `j` is interpreted as the address of an integer.  With `*j` we can denote
  the value stored at address `j` (the value `j` points to).
- With `sizeof()` we get the size of a variable of a type in bytes:
    - `sizeof(i)`, `sizeof(j)` gives the size of variables `i` and `j`
      respectively.
    - `sizeof(int)`, `sizeof(int *)` gives the size of types `int` and `int *`
      respectively.

Example: Modify a variable indirectly
=====================================

:import: session08/pointers1.c

Exercise:

- Compile and run the program. Check the exit code.
- Modify the program such that it prints the value of `i` before and after it
  gets changed indirectly.  Also print:

  - the address of `i`,
  - the size of `i` and the size of `int`,
  - the size of `j` and the size of `int *`.

  In your code:

  - Use a forward declaration for function `printf`.
  - Use the `%d` placeholder to print a integer value.
  - Use the `%p` placeholder to print an address.  Note that `%p` expects a
    pointer to `void` so you need a cast (even if it will work on most
    computers without cast).
  - Use `%zu` to print size of type or variable.

Example: Call by reference
==========================
In the following example function foo is supposed to change it argument to
value `5`.  An experienced Fortran programmer (but new to C) tries the
following:

:import: session08/pointers3.c

- Why is this not working?
- Make it work by applying the pattern: Call by reference is realized by
  passing a pointer by value.