Cant find this bug, can you?

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Summary:

Small movement program with an odd bug.

Cant find this bug, can you?

symaxian 25 Nov 2008 05:11

:DelVar H
:
:Repeat H=45
:
:Text(G6+1,(F-1)4+2,"θ"
:
:Repeat Ans
:getKey→H
:End
:
:If H=24 and F>1 or H=26 and F<23
:Then
:H-25+F
:If L1(G23+Ans)<4                          //checks if the map piece isnt "solid"
:Ans→K
:End
:
:If H=25
:Then
:If L1((G-1)23+F)<4
:G-(G>1)→L
:End
:
:If H=34
:Then
:If L1((G+1)23+F)<4
:G+(G<8)→L
:End
:
:L1(G23+F)
:If Ans
:Then
:sub(",F()Y-^.{}[]I/O:",Ans,1            //replaces the character over the map piece,
:Else
:"   "                                             //or overwrites it with spaces
:End
:Text(G6+1,(F-1)4+2,Ans
:
:K→F
:L→G
:
:If H=31
:prgmMENU
:
:If H=21
:Then
:L1(23G+F)→J                                  //map piece
:If J=2
:Then
:prgmθLOADSCR                               //just clears and creates borders on screen
:prgmMAPCHOOS                              //load an adjacent map
:End
:If J=3
:prgmFISHING                                 //leveling fishing skill, anyone?
:End
:
:End

The code is for movement in a 23x9 character map on the graphscreen, char is theta, F and G for X and Y.
L1 is the map data, 207 numbers for the map space entry and 23 zeros so as not to cause a DIM error.

When opened from the game's main menu, the first arrow key pressed sends the character to an odd part of the screen, not close to an adjacent position, after this first glitchy move the program moves the character fine.
Coming from the main menu program:
F=12
G=5

H=getKey, of course

"I want you" to find the problem, seriously ive scoured it completely and cant find why it does this.

Re: Cant find this bug, can you?

DarkerLine 25 Nov 2008 06:23

K and L are not initialized. When an arrow key is pressed, the program will either update K to be F+/-1, or update L to be G+/-1. The other will remain uninitialized until K and L are stored to F and G, causing the character to jump. After this point it will always be true that F=K and G=L at the start of the loop, so nothing out of the ordinary will happen.

Add F→K and G→L at the beginning of this program to fix things.