========================
Scanner for Integers (1)
========================

Now it gets a bit more complex. Instead of individual digits, whole integer
values should now be recognized in the input. You will be given a template for
this. First, you should test it, and then we'll take a closer look at the
details.

Change or add to your program as follows:

---- CODE(file=session01/page05/ex1.abc, type=abc, linenumbers) ----------------
@ <stdio.hdr>

fn main()
{
    while (true) {
        local ch: int = getchar();
        if (ch >= '0' && ch <= '9') {
            local val: int = 0;
            while (ch >= '0' && ch <= '9') {
                val *= 10;
                val += ch - '0';
                ch = getchar();
            }
            printf("integer with value %d\n", val);
        } else if (ch == EOF) {
            break;
        } else {
            printf("ch = %d -> '%c'\n", ch, ch);
        }
    }
}
--------------------------------------------------------------------------------

Tasks
=====
- Test the program with an input such as `abc123xy42`. Then it should correctly
  recognize that the integer values `123` and `42` occur:
  
  ---- CODE(type=txt) ----------------------------------------------------------
  MCL:session1 lehn$ ./a.out
  ab123xy42
  ch = 97 -> 'a'
  ch = 98 -> 'b'
  integer with value 123
  ch = 121 -> 'y'
  integer with value 42
  ------------------------------------------------------------------------------
  
  But the program is not working correctly yet. The `'x'` was "swallowed". In
  general, after each number, the following character is swallowed. We will
  address this later.
  
- Now consider the part of the program that detects numbers in the input and
  ensures that the variable `'val'` subsequently contains the corresponding
  numeric value. Consider this part:
  
  ---- CODE(type=abc) ----------------------------------------------------------
  local val: int = 0;
  while (ch >= '0' && ch <= '9') {
      val *= 10;
      val += ch - '0';
      ch = getchar();
  }
  ------------------------------------------------------------------------------
  
  Explain to your neighbor (or let us explain to you) why, when inputting the
  sequence of digits `'1'`, `'2'`, `'3'`, the variable `'val'`:
  
  - after the first loop iteration, has the value `1`,
  - after the second loop iteration, has the value `12`,
  - after the third loop iteration, has the value `123`.
  
- Use the `*=` and `+=` operators in the while loop.
  
- Now explain to your neighbor why a character is swallowed after each number.
  How the problem can be solved will be seen in the next step.