=============
Some basic IO
=============

---- CODE(file=session01/page03/ex1.abc, type=abc, linenumbers) ----------------
@ <stdio.hdr>

fn main() {
    while (true) {
        putchar(getchar());
    }
}
--------------------------------------------------------------------------------

In `<stdio.h>`, the functions `getchar` and `putchar` are declared:

- The `getchar` function reads a character from the keyboard and returns it as a
  return value.
- The `putchar` function expects a character as an argument and displays it on
  the screen.

The program shown above, `ex1.abc`, does the following in an infinite loop:
Read a character and then output it, read a character and then output it, and
so on.

Tasks
=====

- Write the program in your preferred editor. Compile and execute it. Be aware
  of the following: Characters are obviously not immediately displayed but only
  after you press Return. For example, if you input `'a'`, `'b'`, `'c'`, and
  then `Return`, you will get the following output:

  ---- CODE (type=txt) ---------------------------------------------------------
  MCL:session1 lehn$ ./a.out
  abc
  abc
  ------------------------------------------------------------------------------

  You can use `Control-C` to (forcefully) terminate the program since it runs an
  infinite loop.

- Our programs run within the shell. Therefore, the above
  statements about getchar and putchar were incorrect. More accurately (in terms
  of fuzzy logic) is:

  - `getchar` does not get input from the keyboard but from the shell.
  - `putchar` does not write characters to the screen but passes them to the
    shell for output.

  By default, the shell only forwards input to our program after you press
  Return. The purpose is to allow you to correct your input (for example, with
  Backspace) before pressing Return.

- You can use the shell command `stty` to change this behavior so that input is
  immediately forwarded to the program:

  ---- CODE (type=txt) -----------------------------------------------------------
  MCL:session1 lehn$  stty -icanon min 1
  MCL:session1 lehn$  ./a.out
  aabbcc
  --------------------------------------------------------------------------------
  
  The shell is now "unusable" (we naturally want to be able to correct our
  inputs before pressing Return). Therefore, you should close and restart the
  terminal.

- In the program, the keyword `true` was used as a condition. Internally, `true`
  is replaced with `1` by the compiler. Generally, any integer value can be used
  as a condition. The rule is "Zero is `false`, and everything else is `true`."
  
  We test this using the workflow "Edit and save -> Compile -> Test":

  - Change `true` to `42`.
  - Change `true` to `2 > 1`.