New coder help Family Basic

[Phosis]

Hello everyone. I am trying to work may way through and understand the code of one of the example problems in the Family Basic manual, namely the KNIGHT game. I am just having trouble breaking down and understanding what the different parts of the code are doing.

I know its a bit vague to ask but is anyone able to sort of assist me with this? Ultimately I am trying to modify it to make a chess game, so I guess the most important part is understanding how the movement through the grid works.

Thank you

[P]

Well how much BASIC do you know? Have you completed the tutorial part of the manual and learned the basics?
I don't have time now but I can look at the code later.

[UglyJoe]

I'll take a look, too, and post some commented source code.  Between P's analysis and mine hopefully you'll be able to see what it's doing

A chess game will be a bit ambitious, but I think it would be possible (without a "vs CPU" mode) if you use the extra RAM available in Family Basic V3.

[Phosis]

Hey guys,

Thank you both.

I am just learning BASIC. I figured out how arrays and multi-dimensional arrays work yesterday. I have worked through the tutorials in the book and am now getting to these programs.

[theoakwoody]

When you finish the game can you share the audio file?

[UglyJoe]

Here are my comments on the code.  I was hoping to go a bit more in-depth, but haven't had much time so figured I'd post what I have now instead of keeping you waiting.  If you have any questions feel free to ask

// Turn on the BG and define player sprites/colors
10 VIEW:CGEN 3:CGSET 1,1
20 DEF SPRITE 0,(0,0,0,0,0)=CHR$(&HC7)
30 PALETS 0,13,&H16,&H27,2
40 DEF SPRITE 2,(0,0,0,0,0)=CHR$(&HD7)
50 DEF SPRITE 1,(1,0,0,0,0)=CHR$(&HC7)
60 PALETS 1,13,&H16,&H17,4
70 DEF SPRITE 3,(1,0,0,0,0)=CHR$(&HD7)
80 SPRITE ON
// HX an HY arrays hold the X and Y positions for player 1 (0) and player 2 (1)
90 DIM HX(1),HY(1)
// X and Y arrays are defining the valid moves a Knight can make
// B is a two-dimensional array holding the state of our 8x8 board
100 DIM X(7),Y(7),B(7,7)
// Populate possible Knight moves into X and Y arrays
110 X(0)=-1:Y(0)=-2
120 X(1)=-2:Y(1)=-1
130 X(2)=-2:Y(2)= 1
140 X(3)=-1:Y(3)= 2
150 X(4)= 1:Y(4)= 2
160 X(5)= 2:Y(5)= 1
170 X(6)= 2:Y(6)=-1
180 X(7)= 1:Y(7)=-2
// C is controlling whose turn it is (0 or 1)
// init player 1
190 C=0:GOSUB 250
// init player 2
200 C=1:GOSUB 250
// compact way of saying "if c is 1, make c 0, if c is 0, make c 1"
// (or 'set C to the other player')
// this is how the game makes players "take turns"
210 C=1+(C=1)
220 GOSUB 390
230 IF F=-1 THEN 560
240 GOTO 210
// Player initialization
// Start current player at 0,0. "Finished" flag is reset.
250 X=0:Y=0:F=0
// jump to player-input routine
260 GOSUB 440
// player made an invalid move, so make a sound and try again
270 IF F=1 THEN PLAY"T1O3C2":F=0:GOTO 260
// if the player pressed A then we now know it was a valid move, so we're done with this turn
// should return to calls made at 190 or 200 or (usually) 220
280 IF T=8 THEN RETURN
// process d-pad input when choosing initial player locations
// player pressed 'down' on d-pad
// increment Y value but don't let it go beyond the edge of the board (beyond 7)
290 IF S=4 THEN Y=Y+1:IF Y>7 THEN Y=7
// player pressed 'up' on d-pad
// decrement Y value but don't let it go beyond the edge of the board (beyond 0)
300 IF S=8 THEN Y=Y-1:IF Y<0 THEN Y=0
// some obtuse math here to determine whether to increment or decrement X
// S=1 evaluates to -1 (true) if player pressed 'right' on d-pad
// S=1 evaluates to 0 (false) if player did not press 'right' on d-pad
// similar logic for S=2 but with 'left' on d-pad
// so depending on whether left or right was pressed, we'd add or subtract 1 from X
// (or we'd add or subtract 0 if neither was pressed)
310 X=X+(S=1)-(S=2)
// bounds checking (keeps X between 0 and 7)
320 X=-X*(X>0)+(X>7)
// player's move won't really be done until they press 'A' on a valid square, so update sprite and wait for input again
330 GOTO 260
// start of a loop, but we usually start at 390 (via 220)
// this loop checks to see if the player has any valid moves to make
340 GOSUB 440:F=0
350 IF T=8 THEN RETURN
// if user pressed a button other than 'A', treat it as if they pressed 'down' on the d-pad
360 IF S=0 THEN S=4
// if user pressed 'up' on d-pad, decrement possible-move counter (wrapping around if necessary)
370 IF S=8 THEN N=N-1:IF N<0 THEN N=7
// if user pressed 'down' on d-apd, increment possible-move counter (wrapping around if necessary)
380 IF S=4 THEN N=N+1:IF N>7 THEN N=0
// modify current player's X and Y for current N value within the X and Y arrays
390 X=HX(C)+X(N):Y=HY(C)+Y(N)
// increment F until we've tried all 8 possible valid moves
// (when jumping from 220, F should be 0)
// if we tried them all, set the Finish flag to -1 (game is over!)
400 F=F+1:IF F>8 THEN F=-1:RETURN
// if this valid move would be out of bounds, go to 360
// (which will increment or decrement N so that we try the next possible move)
410 IF X<0 OR X>7 OR Y<0 OR Y>7 THEN 360
// if this valid move puts the player on a square that's alredy been used, go to 360 (to try the next move)
420 IF B(X,Y)=1 THEN 360
// if we made it here then we found that a valid move is available, so 
430 GOTO 340
// player-input routine (also 'draw-player-sprite' routine')
// Draw the player's sprite at their current X,Y location
// (the extra numbers here are to compensate for pixel dimensions)
440 SPRITE C,136-16*X,16*Y+47
// read the current players controller input (buttons in T, d-pad in S)
450 T=STRIG(C):S=STICK(C)
// if the user didn't make any input, go back and try again (while loop...)
460 IF (S+T)=0 THEN 450
// if the player didn't press the 'A' button then exit the input routine
470 IF T<>8 THEN 540
// otherwise player pressed the 'A' button
// check if the board location has already been used for the curent X,Y
// if so, set F to 1 and return
480 IF B(X,Y)=1 THEN F=1:RETURN
// otherwise B(X,Y) has not been set, so set it now
490 B(X,Y)=1
// store the curent player's X,Y
500 HX(C)=X:HY(C)=Y
// draw the current player's flag at their current location
510 SPRITE C+2,136-HX(C)*16,16*HY(C)+47
// move cursor to player's current location
520 LOCATE 15-2*HX(C),3+2*HY(C)
// draw an asterisk at the location and play a sound
530 PRINT"*":PLAY"T1O3CDEG"
// end-of-turn routine
// hide the player's sprite
540 SPRITE C
// return to whatever got us here via GOSUB
550 RETURN
// end-of-game routine
560 'END ROUTINE
570 LOCATE 3,20:PLAY"T1O3CDET2O4EGAC"
580 IF C=1 THEN PRINT "BLUE ";
590 IF C=0 THEN PRINT "RED ";
600 PRINT "WIN !!":END