Confused about mid() command - Printable Version

Code:

' Open a window and enable double buffering.

set window "Test", 800, 632, false

set redraw off



visible a = "ABCDEF"

visible b

visible c



'   display the letters "B" to "E" inclusive...

b = mid(a, 1, 4)

pln b

'   This works fine...



'   But, when I try to make the third letter "D"

'   an "X"...



'   mid(b, 3, 1) = "X"

'   pln b



'   I get a syntax error on line 17 during compile



'(remove the "remarks" from lines 17 and 18

' to see what I mean...)



system "pause"

Code:

'Console Mode

a = "ABCDEF"



pln "a                  = "+a

pln



'display the letters "B" to "E" inclusive...

b = mid(a,1,4)

pln "MID(a,1,4)         = "+b



'replace D with X

pln "REPLACE D with X   = "+replace(b,"D","X",2)

pln



system "pause"

Code:

'=====================================================

'PACMAN in N7

'Control Key :

'- movement   WASD

'- exit       ESC

'

'Reference :

'Tutorial on QBasic Game Design by Andre van Wyk

'http://petesqbsite.com/sections/tutorials/tutorials/basicgd.htm

'

'Quick Tips on qbasic to N7

'-locate y,x                 - set caret x,y

'-print                      - write

'-mid$()                     - mid

'======================================================

#win32

set window "Pacman",80,60,false,10

set redraw off



'color definition

black  = [0,0,0]

white  = [255,255,255]

yellow = [255,255,0]



'initial Pacman's position

x = 40

y = 10



'maze

maze = []

maze[0] = "########"

maze[1] = "#    # #"

maze[2] = "#  #   #"

maze[3] = "# ## # #"

maze[4] = "#    # #"

maze[5] = "########"



do

    set color black ; cls

    

    'maze

    set color white

    for j=0 to 7

        for i = 0 to 5

            set caret j*10,i*10

            write mid(maze[i],j)

        next

    next

    

    'remember Pacman's position

    posX = x

    posY = y

        

    'control

    if keydown(KEY_W) and y>1   then y=y-10 

    if keydown(KEY_S) and y<60  then y=y+10

    if keydown(KEY_A) and x>1   then x=x-10

    if keydown(KEY_D) and x<80  then x=x+10

    

    'collision detection Pacman and Maze

    if mid(maze[y/10],x/10)="#" then

        x = posX

        y = posY

    endif

    

    'Pacman

    set color yellow

    set caret x,y ; write "C"

    

    redraw

    fwait 10

 until keydown(KEY_ESCAPE,true)