14.7. Example of Input-Output

The following example shows the use of some of the text input-output facilities in a dialogue with a user at a terminal. The user is prompted to type a color, and the program responds by giving the number of items of that color available in stock, according to an inventory. The default input and output files are used. For simplicity, all the requisite instantiations are given within one subprogram; in practice, a package, separate from the procedure, would be used.

    with TEXT_IO; use TEXT_IO;
    procedure DIALOGUE is
       type COLOR is (WHITE, RED, ORANGE, YELLOW, GREEN, BLUE, BROWN);
       package COLOR_IO is new ENUMERATION_IO(ENUM => COLOR);
       package NUMBER_IO is new INTEGER_IO(INTEGER);
       use COLOR_IO, NUMBER_IO; 

       INVENTORY : array (COLOR) of INTEGER := (20, 17, 43, 10, 28, 173, 87);
       CHOICE : COLOR;

       procedure ENTER_COLOR (SELECTION : out COLOR) is
       begin
          loop
             begin
                PUT("Color selected: ");  --  prompts user
                GET(SELECTION);  --  accepts color typed, or raises exception
                return;
             exception
                when DATA_ERROR =>
                   PUT("Invalid color, try again.  ");  --  user has typed
                   NEW_LINE(2);                         --   new line
                   --  completes execution of the block statement
             end;
          end loop;  --  repeats the block statement until color accepted
       end;
    begin --  statements of DIALOGUE; 

       NUMBER_IO.DEFAULT_WIDTH := 5; 

       loop 

          ENTER_COLOR(CHOICE);  --  user types color and new line 

          SET_COL(5);  PUT(CHOICE); PUT(" items available:");
          SET_COL(40); PUT(INVENTORY(CHOICE));  --  default width is 5
          NEW_LINE;
       end loop;
    end DIALOGUE; 

Example of an interaction (characters typed by the user are italicized):

    Color selected:  Black
    Invalid color, try again.   

    Color selected:  Blue
        BLUE items available:         173
    Color selected:  Yellow
        YELLOW items available:        10