Problem with a "test" game

Hi everyone!, I'm new on this forum, and, of course, in blitz programming.
I've been trying to create a little game in blitzplus, but I have found a problem that I can't solve. Could you help me?

The case is that when I try to kill the "enemy navs" they don't disappear, and if they do, the program crashes. I'm sure that this is a very simple problem, but how I'm new in this word, I don't see it. Anyway, thanks a lot.

Does anybody know how to kill the enemies?

Oh, yes, this program structure is the worst in the world, I know it. :-)

If you want to see the code in an editor: http://rapidshare.com/files/77814890/movement_test2.bb


----------


;Variables
Global player.nav = New nav
Global bullet.ball = New ball
Global enemy.nav = New nav
Global leftkeyr = 1
Global randomnumber
Global randomgrade = 1000
Global maximumx,maximumy,minimx,minimy
Const rightkey = 205
Const leftkey = 203
Const upkey = 200
Const downkey = 208
Const spacekey = 31
Const esckey = 1
Const ball1$ = ""
Const nav1$ = "<-*->"
Const startx% = 400
Const starty% = 300
Const startvel = 5
;-------------------------------------------------------------------------

;Types
Type nav
Field x,y
Field vel
Field navimage$

End Type
player\x = startx
player\y = starty
player\vel = startvel
player\navimage = nav1$

Type ball
Field x,y
Field vel
Field ballimage
End Type


;-------------------------------------------------------------------------


;#########################################################################
;Main loop
Graphics 800,600,16,2
SeedRnd MilliSecs
SetBuffer BackBuffer ()
While Not KeyHit (esckey)
Cls
userinput ()
drawplayer ()
drawbullets ()
drawenemies ()
deletenemies ()

Flip
Delay 20
Wend
End
;#########################################################################


;=========================================================================
;Functions ;
;=========================================================================


;draw player
Function drawplayer ()
Text player\x,player\y,player\navimage,True,True
End Function

;-------------------------------------------------------------------------

;draw bullets
Function drawbullets ()
For bullet.ball = Each ball
If (bullet\y > -10) Then
Text bullet\x,bullet\y,"*",True,True
bullet\y = bullet\y - bullet\vel
End If
Next

End Function

;draw enemies
Function drawenemies ()
randomnumber = Rnd(0,randomgrade)
If randomnumber < 5 Then
enemy.nav = New nav
enemy\navimage = "(OO)"
enemy\x = Rnd (20,790)
enemy\y = Rnd (20,590)
End If
For enemy.nav = Each nav
Text enemy\x,enemy\y,enemy\navimage,True,True
Next
randomgrade = randomgrade - 1

End Function

;eliminate enemies
Function deletenemies ()
For bullet.ball = Each ball
For enemy.nav = Each nav
If (enemy\x < (bullet\x + 10)) And (bullet\x > (bullet\x - 10)) Then
Delete enemy
End If
Next
Next
End Function


;-------------------------------------------------------------------------

;User input
Function userinput ()
If KeyDown (leftkey) Then
player\x = player\x - player\vel
End If
If player\x <=23 Then
player\x = 23
End If

If KeyDown (rightkey) Then
player\x = player\x + player\vel
End If
If player\x >= 777 Then
player\x = 777
End If

If KeyDown (upkey) Then
player\y = player\y - player\vel
End If
If player\y <=5 Then
player\y = 5
End If

If KeyDown (downkey) Then
player\y = player\y + player\vel
End If
If player\y >= 595 Then
player\y = 595
End If

If KeyDown (31) Then
bullet.ball = New ball
bullet\x = player\x
bullet\y = player\y
bullet\vel = 10
bullet\ballimage = "*"
End If


End Function

;=========================================================================



Again, thanks!

The reason is because in your delete enemies function the first 'enemy' the bullet collides with is the 'player' 'nav' type and so it deletes the 'player' 'nav' type instance which means when the code gets to the userinput function the 'player' instance is now null so it crashes as soon as it is referred to.

What you need to do to fix it is to prevent the player's own bullets from colliding with it.

Also, if I were to give advice I would suggest not using a global type called 'player' but simply have a field within the 'nav' type object which flags whether the nav is an enemy or a player (you could even do the ball/bullet in there as well).

Thanks you a lot! now it works! Anyway, is sure that this "game" needs a lot of reviews, but this is a good step to make it work.

Ruben