========================
Scanner for Integers (2)
========================

The issue with swallowed characters after a sequence of digits has been
resolved in the following adjustment:

---- CODE(file=session01/page06/ex1.abc,type=abc,linenumbers) ------------------
@ <stdio.hdr>

fn main()
{
    local ch: int = getchar();
    while (true) {               
        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);
            ch = getchar();
        }
    }
}
--------------------------------------------------------------------------------

Tasks
=====

- Test that no characters are swallowed anymore.
  
- In the program, there are two significant changes:
  
  - The variable `ch` is now declared before the while loop. The scope of the
    `ch` variable is now the entire function. The places where `ch` is
    overwritten are in lines 12, 19.
  
  - In the `else` branch of the `if` statement, `getchar` is now also called
    (line 19), and `ch` is overwritten. Test why this is necessary by
    commenting out this line, i.e., modifying it to
  
    ---- CODE(type=abc) --------------------------------------------------------
    // ch = getchar();
    ----------------------------------------------------------------------------
  
    Then test the program again. Explain to your neighbor what goes wrong and
    why. Then revert the change.
  
- The program should now also treat the `'+'` character specially. Add the
  following code after line 14:
  
  ---- CODE(type=abc) ----------------------------------------------------------
  } else if (ch == '+') {    
      printf("PLUS\n");                       
      ch = getchar();                     
  ------------------------------------------------------------------------------
  
- Test the program, for example, with `12 + 4`.
  
- Modify the program so that:
  
  - `'*'` produces the output ASTERISK.
  - `'('` produces the output LPAREN (for "Left Parenthesis").
  - `')'` produces the output RPAREN (for "Right Parenthesis").
  - `';'` produces the output SEMICOLON."