From:	"Karl Martens" <martensk AT telusplanet DOT net>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Detecting Arrow key presses
Date:	Tue, 13 Oct 1998 07:35:52 -0600
Organization:	TELUS Communications Inc.
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References:	<4661cac DOT 3622aaa3 AT aol DOT com> <JVBU1.609$Ni2 DOT 121742 AT news DOT cwix DOT com>
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Chris Broome wrote in message ...
>DoctorXV AT aol DOT com wrote in message <4661cac DOT 3622aaa3 AT aol DOT com>...
>>how do I get C++ to detect arrow key presses? I use Turbo C++ 3.0
>
>This works very well in a loop:
>
>#include <conio.h>
>
>/* These are just a few ASCII values for the keys hit.*/
>#define    ENTER    13
>#define    ESC    27
>#define    UP    72
>#define    DOWN    80
>#define    LEFT    75
>#define    RIGHT    77
>#define    BACKSPACE    8
>#define    TAB    9
>#define    SPACE    32
>
>void main()
>{
>char key;
>while(SomeCondition)
>    {
>    if (kbhit())        /* first detect if the keyboard was hit */
>        {
>        key=getch();    /* if it was, then get what key was hit */
>        if (key==UP) ....  /* if up was hit, do something*/
>        }
>    }
>}


    This is very close to right and it does work but the ascii values used
are those of characters.  That is to say UP == 'H' == 72 and DOWN == 'P' =
80.  The difference between say the user pressing 'P' and the down key is
that getch () first sends a 0 and then the corresponding UP | DOWN | LEFT |
RIGHT value.  The reason this above code will work is that kbhit () will
return != 0 when something is in the keyboard buffer, thus the code inside
the if (kbhit ()) {} will exicute twice for the arrow keys.  Furthermore,
the user will be able to manipulate the object you wish to move by simply
pressing 'H' | 'P' |...

    A better way to do this would be to have your code look something
like...

void main ()
{
  // declare all variables
  char ch;

....   // what ever you like

  do  // ensure code inside loop is exicuted at least once,  if this is not
desired put the while condition here
  {
    if (kbhit ())  // if keypressed then interpret it...
   {
      ch = getch ();
      switch (ch)
      {
         case 'a':              // put in whatever code you like
                         break;
         case 'P':              // put in whatever code you like
                          break;
        case 0:     ch = getch ();
                          if (ch == UP)
                          {
                                                  // then up key pressed...
                          }
                          else if (ch = DOWN)
                          {
                                                  // then down key
pressed...
                          }
                                                  // Note no break here this
is because a 0 isn't only sent for the arrow keys so
                                                  // implementing the code
in this manner will allow exicution continue into the
                                                  // default portion of the
switch, detecting an invalid keystroke.  Only works if the
                                                  // case 0 is directly
above the default case....
          default:                            // an invalid key has been
pressed take whatever action you like....
                        break;
      }
   }
  } while (whatever);  //  ensure this condition becomes true at some
point...
}


    The above code will guarantee the code you wish to exicute on the arrow
commands are only exicuted when the arrow keys are infact pressed.  Note
you'll still need the topmost code's includes and defines.



Karl Martens

May the force be with you!! :-)

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