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From: aig@i.cc.purdue.edu (Doug Crabill)
Newsgroups: comp.sys.cbm
Subject: C-Power bug ???
Message-ID: <1688@i.cc.purdue.edu>
Date: Sun, 7-Dec-86 21:03:30 EST
Article-I.D.: i.1688
Posted: Sun Dec  7 21:03:30 1986
Date-Received: Mon, 8-Dec-86 05:39:07 EST
Distribution: net
Organization: Unidue Purversity
Lines: 53
Keywords: C-Power, bug


	I am writing a game in C-Power (please hold all applause until the end
of the article) and have run into a bit of a problem.  I can't be sure if it is
a problem with the way I have the code set up or if it is a problem with
C-Power.  I figured I would post what I have in hopes that some kind soul out 
there could spot a problem.  I know there are other ways to write this bit of 
code, but I really want to know why it doesn't work as it is.


--------------------------------This is it-------------------------------------
/*
   This program checks joyport 1 and updates a sprite on the screen according
   to the direction of the joystick.  Real simple right?
*/

#include <stdio.h>
main()
{
	struct tank {
		char *x;	/* x coordinate		*/
		char *y;	/* y coordinate		*/
		float a;	/* doesn't matter here  */
		char *sp;	/* sprite image pointer */
	};
	char *joy1;	/* joyport location */
	char j; 	/* temporary copy of *joy1 */
	char *enable;	/* sprite enable location  */
	struct tank *pl1;	/* the sprite used in this program */
	pl1->x = 53248;  *pl1->x = 30;
	pl1->y = 53249;  *pl1->y = 100;
	pl1->a = 0.0;
	pl1->sp = 2040;  *pl1->sp = 192;  /* set the sprite pointer */
	joy1 = 56320; 	/* set joyport location */
	enable = 53269; /* set sprite enable location */
	*enable = 1;	/* enable sprite 1 */

	/* set up an infinite game loop */
	for (;;) {
		/* 
		   what happens here is that the sprite will not move unless
		   the joystick is pushed up (the first case) and when this
		   happens, ALL of the ifs below are executed, so the sprite
		   goes up, down, left, right (sounds like aerobics eh?)
		   I've printed out j as I go and it is as it should be.
		*/

		j = 15 - (*joy & 15);
		if ((j&1 == 1) && ((*pl1->y) > 50)) (*pl1->y)--;  /* up    */
		if ((j&2 == 2) && ((*pl1->y) < 226)) (*pl1->y)++; /* down  */
		if ((j&4 == 4) && ((*pl1->x) > 24)) (*pl1->x)--;  /* left  */
		if ((j&8 == 8) && ((*pl1->x) < 250)) (*pl1->x)++; /* right */
	}
}