# Writing an Adventure Game 03

Continuing from yesterday's Writing an Adventure game post, today we will solve the problem of the player walking off the edge of the map and crashing the game.  It is a simple fix to check that the player's movement will not take him/her beyond the allowed boundary.

In our PROC_executeCommand() procedure, you will find some code similar to the following:

WHEN com\$ = "n" OR com\$ = "north"
IF y%<3 THEN

y% += 1
ELSE
PRINT
gridError\$
ENDIF

Which, roughly translated means:

WHEN THE PLAYER WANTS TO MOVE NORTH
IF THE PLAYER IS NOT AT THE EDGE OF THE MAP
MOVE NORTH
ELSE
DISPLAY AN ERROR MESSAGE

A similar construction occurs at all of the compass directions.

 A simple fix to check for walking off the edge of the map.  In fact, you could allow the player to move off, but wrap around so that they appear on the other side of the map instead.

Source code follows:

REM an adventure game in BB4W
REM by Mr Street

REM version 1.0.0.1 setting up the world
REM version 1.0.0.2 moving around the world
REM version 1.0.0.3 fixing it so you can't walk out of the grid

REM let's set up a 'world'

DIM World\$(3,3) : REM creates a 3x3 grid
REM now 'populate' the grid with some space names

PROC_populateWorld
REM now some data about our player
REM player's starting position

x% = 2
y% = 2
REM player's health

health% = 50

PROC_main

DEFPROC_main
LOCAL command\$ : REM user's input
REM the main program
REM repeat until the player is dead

REPEAT

REM show the player's current position

PROC_showCurrent
REM get some input from the player

INPUT "What now? > " command\$
REM deal with user's input

PROC_executeCommand( command\$ )
UNTIL health% <= 0
ENDPROC

DEFPROC_executeCommand( command\$ )
REM deals with the users input

LOCAL com\$, gridError\$
gridError\$ = "You can't go in that direction!" : REM a message for when you move off the grid

com\$ = FN_convlc( command\$ ) : REM convert to lowercase so it is easier

CASE TRUE OF
WHEN
com\$ = "n" OR com\$ = "north"
IF y%<3 THEN

y% += 1
ELSE
PRINT
gridError\$
ENDIF

WHEN
com\$ = "s" OR com\$ = "south"
IF y% >1 THEN

y% -= 1
ELSE
PRINT
gridError\$
ENDIF

WHEN
com\$ = "e" OR com\$ = "east"
IF x%<3 THEN

x% += 1
ELSE
PRINT
gridError\$
ENDIF

WHEN
com\$ = "w" OR com\$ = "west"
IF x%>1 THEN

x% -= 1
ELSE
PRINT
gridError\$
ENDIF

ENDCASE
ENDPROC

DEFPROC_showCurrent
PRINT "You are at the : "World\$(x%, y%)
PRINT "Your health is : "STR\$(health%)
ENDPROC

DEF FN_convlc(A\$)
REM converts to lower case

SYS "CharLowerBuff", !^A\$, LEN(A\$)
= A\$

DEFPROC_populateWorld
REM puts some names of the spaces into the World

LOCAL x%, y%

FOR y% = 1 TO 3
FOR x% = 1 TO 3
NEXT
NEXT
ENDPROC

:
REM the data for our 3x3 grid

DATA "Hills",  "Mountains", "Forest"

DATA "Castle", "Village", "Fields"

DATA "Woods",  "Swamp",  "Lake"

In fact, a slightly improved program would have a constant variable that sets the size of the game world, allowing the programmer to change the size of the game world to any size they desire without breaking this bit.  For the purpose of these posts we shall keep the size of the world fixed at '3', however I might be tempted to code like this instead:

REM an adventure game in BB4W
REM by Mr Street

REM version 1.0.0.1 setting up the world
REM version 1.0.0.2 moving around the world
REM version 1.0.0.3 fixing it so you can't walk out of the grid
REM  - alternative version -

REM let's set up a 'world'

SIZE% = 3 : rem <--- sets the size of the world
DIM World\$( SIZE%, SIZE% ) : REM creates a 3x3 grid
REM now 'populate' the grid with some space names

PROC_populateWorld
REM now some data about our player
REM player's starting position

x% = 2
y% = 2
REM player's health

health% = 50

PROC_main

DEFPROC_main
LOCAL command\$ : REM user's input
REM the main program
REM repeat until the player is dead

REPEAT

REM show the player's current position

PROC_showCurrent
REM get some input from the player

INPUT "What now? > " command\$
REM deal with user's input

PROC_executeCommand( command\$ )
UNTIL health% <= 0
ENDPROC

DEFPROC_executeCommand( command\$ )
REM deals with the users input

LOCAL com\$, gridError\$
gridError\$ = "You can't go in that direction!" : REM a message for when you move off the grid

com\$ = FN_convlc( command\$ ) : REM convert to lowercase so it is easier

CASE TRUE OF
WHEN
com\$ = "n" OR com\$ = "north"
IF y%<SIZE% THEN

y% += 1
ELSE
PRINT
gridError\$
ENDIF

WHEN
com\$ = "s" OR com\$ = "south"
IF y% >1 THEN

y% -= 1
ELSE
PRINT
gridError\$
ENDIF

WHEN
com\$ = "e" OR com\$ = "east"
IF x%<SIZE% THEN

x% += 1
ELSE
PRINT
gridError\$
ENDIF

WHEN
com\$ = "w" OR com\$ = "west"
IF x%>1 THEN

x% -= 1
ELSE
PRINT
gridError\$
ENDIF

ENDCASE
ENDPROC

DEFPROC_showCurrent
PRINT "You are at the : "World\$(x%, y%)
PRINT "Your health is : "STR\$(health%)
ENDPROC

DEF FN_convlc(A\$)
REM converts to lower case

SYS "CharLowerBuff", !^A\$, LEN(A\$)
= A\$

DEFPROC_populateWorld
REM puts some names of the spaces into the World

LOCAL x%, y%

FOR y% = 1 TO SIZE%
FOR x% = 1 TO SIZE%
NEXT
NEXT
ENDPROC

:
REM the data for our 3x3 grid

DATA "Hills",  "Mountains", "Forest"

DATA "Castle", "Village", "Fields"

DATA "Woods",  "Swamp",  "Lake"