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Help with arrays and X and Y
Post by Megaman27 on Apr 12th, 2013, 5:25pm

Hi, I need help with a program I'm making in Basic. It is a game where the user must "eat" the "prey" by moving the character around the screen. I've used two arrays to store the X and Y positions of the 10 Prey:
dim Prey_X%(10)
dim Prey_Y%(10)
rem repeating the cycle

numPrey% = 10
rem set up prey
for n% = 1 to numPrey%
read Prey_X%( n% )
read Prey_Y%( n% )
next

data 11,5,6,3,14,20,20,12,8,10,15,15,12,6,5,2…

And now I need help with making the character eat the "Prey". I want for the X and Y positions of the character to be compared to the X and Y positions of the different prey; and if they match, the prey would disappear and the score would increase. I have already done the scoring part, but what I'm stuck on is what I need to write so that the X and Y positions of each are compared. I have put:
" if x%=Prey_X%( n%) but it says that it is bad subscript. Can any1 help?
p.s. I'm a beginner programmer so I not looking for anything too complex. Is it another array I need to use or are the values wrong?
Re: Help with arrays and X and Y
Post by admin on Apr 12th, 2013, 9:30pm

on Apr 12th, 2013, 5:25pm, Megaman27 wrote:
I have put:
if x%=Prey_X%( n%) but it says that it is bad subscript. Can any1 help?

If it reports Bad subscript then the value of n% must either be negative or greater than 10 (in the case when you have DIMensioned the array with a maximum subscript of 10). When the error occurs check the value of n%.

There's nothing particularly wrong with the method you are using. It won't be terribly fast but that may not matter. An alternative approach might be to use a 2-dimensional array corresponding to the grid of positions that the 'prey' can occupy; then each element of the array can hold a value corresponding to what is present at that location. Then the test is very easy:

Code:
  IF grid(x%,y%) <> 0 THEN....

If your prey are positioned at character coordinates then you could simply test the character at the specified coordinates:

Code:
  IF GET$(x%,y%) <> " " THEN ....

Richard.
Re: Help with arrays and X and Y
Post by Megaman27 on Apr 13th, 2013, 2:56pm

ok, but I'm still not entirely sure how the n% could be more than 10 (I put for n%=1 to 10 )?
And I'm not sure about how to make the co-ords of each get compared. I tried:

if (x%,y%) = (Prey_X%(n%), Prey_Y%(N%))

But it either says I'm missing a bracket or, again, it's bad subscript. I know that "tab" is inapplicable, so is there another command that I need to use, or is the above code incorrect?
Re: Help with arrays and X and Y
Post by Megaman27 on Apr 13th, 2013, 3:46pm

oh and can you explain how I would apply the 2-d Array please?

I've gotten so far as:

dim PreyPos (2,10)
PreyX% (10) = 11,6,14,20,8,15,12,5,13,9
PreyY% (10) = 5,3,20,12,10,15,6,20,13,7

But I think I've made an error
Re: Help with arrays and X and Y
Post by Megaman27 on Apr 13th, 2013, 3:49pm

or is it something like:

dim PreyPos (2,10)
PreyPos (0,1)=
Re: Help with arrays and X and Y
Post by admin on Apr 13th, 2013, 4:33pm

on Apr 13th, 2013, 2:56pm, Megaman27 wrote:
I'm still not entirely sure how the n% could be more than 10 (I put for n%=1 to 10 )?

Maybe you've accidentally accessed the array after the FOR..NEXT loop has finished (on exit from the loop n% will be 11).

Quote:
And I'm not sure about how to make the co-ords of each get compared. I tried:
if (x%,y%) = (Prey_X%(n%), Prey_Y%(N%))

Do it like this:

Code:
IF x% = Prey_X%(n%) AND y% = Prey_Y%(n%) THEN...

Quote:
can you explain how I would apply the 2-d Array please?

Suppose the grid of possible locations has 40 columns and 25 rows, then you would define the array as follows:

Code:
DIM grid%(39,24)

Or if you're short of memory (e.g. you're using the trial version) use a byte array:

Code:
DIM grid&(39,24)

To initialise the array with the prey positions:

Code:
FOR prey% = 1 TO 10
  READ x%,y%
  grid%(x%,y%) = prey%
NEXT prey%

To test if the character has landed on a prey:

Code:
IF grid%(x%,y%) <> 0 THEN....

To 'eat' the prey (so it isn't there any more):

Code:
grid%(x%,y%) = 0

Richard.
Re: Help with arrays and X and Y
Post by Megaman27 on Apr 13th, 2013, 4:56pm

Ok, sorry to bother you but I have one final Question I promise!
I have almost finished the program I was making as a project, but the last problem I have is that the program says that it isn't in a Repeat Loop. Could you please look at my program and identify my fault, and I promise I'll leave you alone from now on!!

x%=20
y%=15

sprite$ =chr$(240)
prey$ =chr$(241)


score%=0
samexy%=false

print score%

dim Prey_X%(10)
dim Prey_Y%(10)
rem repeating the cycle

numPrey% = 10
rem set up prey
for n% = 1 to numPrey%
read Prey_X%( n% )
read Prey_Y%( n% )
next

data 4,5,6,3,14,20,20,12,8,10,15,15,12,6,5,20,10,10,9,7



rem display the prey
for A%=1 to 10
print tab(Prey_X%( A% ),Prey_Y%( A% ))chr$(241)
next



repeat

rem get the user's key
g%= get

rem Find out the key
if g%=136 then
rem if it is left
if x%>5 then
x%=x% - 1
endif
endif
print tab(x%+1,y%)chr$(32)




if g%=137 then
rem if it is right
if x%<35 then
x%=x% + 1
endif
endif
print tab(x%-1,y%)chr$(32)

if g%=138 then
rem if it is down
if y%<23 then
y%=y%+1
endif
endif
print tab(x%,y%-1)chr$(32)

if g%=139 then
rem if it is Up
if y%>2 then
y%=y%-1
endif
endif
print tab(x%,y%+1)chr$(32)



print tab(x%,y%)chr$(240)




rem Scoring system
for index% = 1 to 10
if Prey_X%(index%) = x% and Prey_Y%(index%) = y% then
samexy$ = true
endif

if samexy%=true then
score%=score%+10
endif

until score%=100 rem The place highlighted "Not in a REPEAT loop"

if score%=100 then
print "Well Done, You Have Killed All The Prey! "
stop
endif

Re: Help with arrays and X and Y
Post by Megaman27 on Apr 13th, 2013, 5:21pm

Oh sorry I sent it wrong. Thanks to your help I've finished the program. Thank you Richard grin
You are welcome to try it out if you want:


rem Turn off typing cursor

mode 6

off

rem The Sprite
vdu 23,240,36,62,106,255,195,126,36,36

rem The Prey
vdu 23,241,96,32,32,60,60,60,20,20

x%=20
y%=15

sprite$ =chr$(240)
prey$ =chr$(241)


score%=0
samexy%=false

print tab(0,0) score%

dim Prey_X%(10)
dim Prey_Y%(10)


numPrey% = 10
rem set up prey
for n% = 1 to numPrey%
read Prey_X%( n% )
read Prey_Y%( n% )
next

data 16,5,6,7,14,20,20,12,8,10,15,15,12,6,5,20,10,10,9,7



rem display the prey
for A%=1 to 10
print tab(Prey_X%( A% ),Prey_Y%( A% ))chr$(241)
next


rem repeating the cycle
repeat

rem get the user's key
g%= get

rem Find out the key
if g%=136 then
rem if it is left
if x%>5 then
x%=x% - 1
endif
endif
print tab(x%+1,y%)chr$(32)




if g%=137 then
rem if it is right
if x%<35 then
x%=x% + 1
endif
endif
print tab(x%-1,y%)chr$(32)

if g%=138 then
rem if it is down
if y%<23 then
y%=y%+1
endif
endif
print tab(x%,y%-1)chr$(32)

if g%=139 then
rem if it is Up
if y%>2 then
y%=y%-1
endif
endif
print tab(x%,y%+1)chr$(32)



print tab(x%,y%)chr$(240)




rem Scoring system

for index% = 1 to 10
if Prey_X%(index%) = x% and Prey_Y%(index%) = y% then
samexy% = true
print tab(Prey_X%(index%),Prey_Y%(index%)) chr$(240)
endif
next

if samexy%=true then
score%=score%+10
print tab(0,0) score%
endif

samexy%=false
rem until score%=100 rem The place highlighted "Not in a REPEAT loop"

if score%=100 then
print "Well Done, You Have Killed All The Prey! "
stop
endif

until false





rem turn cursor on
on

I know it isn't exactly complex, but I plan to add new features later on. Anyway, thanks again Richard and best of luck in future programming!
Re: Help with arrays and X and Y
Post by DDRM on Apr 16th, 2013, 08:34am

Hi Megaman,

I love the llamas/camels/prey!

There are a few minor problems with your code, still.

1) If you go near the prey, sometimes it disappears before you have eaten it: I suspect it's to do with the writing of spaces when you move the monster.

2) You can eat the same prey several times, if you move back and forth over it's place!

It's not a fault, but an alternative way to handle the key input would be to use a CASE statement: this could be a lot more compact.

I hope you'll forgive the presumption, but I've modified your code a little (see below) to include this, and to reset the position of eaten prey to (-1,-1) (off the board) so they can't be eaten again! I've also made the monster visible at the beginning, so you can see where you start. I've also got rid of samexy%, and moved the score write into the block dealing with catching the prey.

Now how about making the prey move, so that you have to plan a route to intercept them? :-)

Best wishes,

David

Code:
      rem Turn off typing cursor
      
      mode 6
      
      off
      
      rem The Sprite
      vdu 23,240,36,62,106,255,195,126,36,36
      
      rem The Prey
      vdu 23,241,96,32,32,60,60,60,20,20
      
      x%=20
      y%=15
      rem show the monster
      print tab(x%,y%)chr$(240)
      
      sprite$ =chr$(240)
      prey$ =chr$(241)
      
      
      score%=0
      samexy%=false
      
      print tab(0,0) score%
      
      dim Prey_X%(10)
      dim Prey_Y%(10)
      
      
      numPrey% = 10
      rem set up prey
      for n% = 1 to numPrey%
        read Prey_X%( n% )
        read Prey_Y%( n% )
      next
      
      data 16,5,6,7,14,20,20,12,8,10,15,15,12,6,5,20,10,10,9,7
      
      
      
      rem display the prey
      for A%=1 to 10
        print tab(Prey_X%( A% ),Prey_Y%( A% ))chr$(241)
      next
      
      
      rem repeating the cycle
      repeat
        
        rem get the user's key
        g%= get
        
        print tab(x%,y%)chr$(32)
        
        
        rem Find out the key
        case g% of
          when 136: if x%>5 then x%-=1
          when 137: if x%<35 then x%+=1
          when 139: if y%>2 then y%-=1
          when 138: if y%<23 then y%+=1
        endcase
        
        print tab(x%,y%)chr$(240)
        
        
        
        
        rem Scoring system
        
        for index% = 1 to 10
          if Prey_X%(index%) = x% and Prey_Y%(index%) = y% then
            rem samexy% = true This is really redundant, isn't it? We can simply move the score bit into this IF
            print tab(Prey_X%(index%),Prey_Y%(index%)) chr$(240)
            Prey_X%(index%)=-1
            Prey_Y%(index%)=-1
            score%+=10
            print tab(0,0) score%
          endif
        next
        
        rem until score%=100 rem The place highlighted "Not in a REPEAT loop"
        
        if score%=100 then
          print "Well Done, You Have Killed All The Prey! "
          stop
        endif
        
      until false
  
   rem turn cursor on
      on