ChessBoard Program

catfish1116 has asked for the wisdom of the Perl Monks concerning the following question:

Working on a 'chessboard' type of script. As you can guess, this is a row/column matrix. Below is the code and subsequent errors:

my @chessboard;
   my @back  = qw(R N B Q K B N R);
   foreach (0..7) {
      $chessboard[0][$_] = "W" . $back[$_};  # White Back Row
      $chessboard[1][$_] = "WP";             # White Pawns
      $chessboard[6][$_] = "BP";             # Black Pawns
      $chessboard[7][$_] = "B" . $back[$_];  # Black Back Row
   }

   while (1) {
      # Print board
      foreach my $i (reverse (0..7))  { # Row
         foreach my $j (0..7)  {        # Column
            if (defined $chessboard[$i][$j])  {
               print $chessboard[$i]$j];
            } elseif ( ($i % 2) == ($j %2) ) {
                  print "..";
            } else {
                  print "  ";
            }
          print " ";  # End of cell
      }  # end of foreach
    print "\n";  # End of row

   print "\nStarting square [x,y]:  ";
   my $move = <>;
   last unless ($move =~ /^\s([1-8]),([1-8)/);
   my  $startx = $1-1;  my $starty = $2-1;

   unless  (defined $chessboard[$starty][$startx]) {
      print "There's nothing on that square!\n";
      next;
   }
   print "\nEnding square [x,y]: ";
   $move = <>;
   last unless  ($move =~ /([1-8]},([1-8])/);
   my $endx = $1-1; my $endy = $2-1;

   #  Put starting square on ending square
   $chessboard[$endy][$endx] = $chessboard[$starty][$startx];
   #  remove from old square
   undef $chessboard[$starty][$startx];
   }
"my" variable @chessboard masks earlier declaration in same scope at .
+/BP_Chap11_Exer1.pl line 29.
"my" variable $i masks earlier declaration in same statement at ./BP_C
+hap11_Exer1.pl line 29.
"my" variable $j masks earlier declaration in same statement at ./BP_C
+hap11_Exer1.pl line 29.
"my" variable @chessboard masks earlier declaration in same statement 
+at ./BP_Chap11_Exer1.pl line 30.
"my" variable $i masks earlier declaration in same statement at ./BP_C
+hap11_Exer1.pl line 30.
Scalar found where operator expected at ./BP_Chap11_Exer1.pl line 30, 
+near "]$j"
        (Missing operator before $j?)
elseif should be elsif at ./BP_Chap11_Exer1.pl line 31.
syntax error at ./BP_Chap11_Exer1.pl line 19, near "$_}"
syntax error at ./BP_Chap11_Exer1.pl line 23, near "}"
Global symbol "$j" requires explicit package name at ./BP_Chap11_Exer1
+.pl line 30.
Global symbol "$i" requires explicit package name at ./BP_Chap11_Exer1
+.pl line 31.
Global symbol "$j" requires explicit package name at ./BP_Chap11_Exer1
+.pl line 31.
Unmatched [ in regex; marked by <-- HERE in m/^\s([1-8]),([ <-- HERE 1
+-8)/ at ./BP_Chap11_Exer1.pl line 42.
[download]

TIA The Catfish

Comment on ChessBoard Program Download Code

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Re: ChessBoard Program by Corion (Patriarch) on Feb 10, 2020 at 22:08 UTC
There are a lot of warnings, and there is one first syntax error at: `Scalar found where operator expected at ./BP_Chap11_Exer1.pl line 30, +near "]$j"` [download] Searching for that string points out this line: `print $chessboard[$i]$j];` [download] The next syntax error is `syntax error at ./BP_Chap11_Exer1.pl line 19, near "$_}"` [download] Searching for that string points to this line: `$chessboard[0][$_] = "W" . $back[$_}; # White Back Row` [download] The line numbers don't match up with your code. Are you sure that you show us the code that produces these error messages?!	[reply] [d/l] [select]
Re: ChessBoard Program by GrandFather (Saint) on Feb 10, 2020 at 22:45 UTC
Always start with the earliest error in the code. In this case it is on line 19: 'syntax error at ./BP_Chap11_Exer1.pl line 19, near "$_}"'. Once you fix that issue there are three or four more of a similar nature. Fix those and the elsif issue and you are left with one final issue due to a missing }. Your indentation is mostly pretty good so it should be easy enough to see where the missing } should go. Optimising for fewest key strokes only makes sense transmitting to Pluto or beyond	[reply]
Re: ChessBoard Program by LanX (Saint) on Feb 10, 2020 at 23:27 UTC
Hello catfish1116 The history of your posts always contain a lot of trivial syntax errors. Errors of a kind one would easily spot if the code was developed step by step. Could it be that you are manually copying the code as a whole from a printed text and ask us to spot the typos? Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply]
Re^2: ChessBoard Program by catfish1116 (Beadle) on Feb 12, 2020 at 19:51 UTC
It is true that I am manually copying the code from a printed text. Early on, it was my own fault for not typing correctly, (those were earlier posts). My more current posts are a result of me typing exactly how the script appears in the books that I am learning from and the code not working, or if the exercises are asking to do the just one function in the program and I try to make it more robust by adding more functionality. I appreciate being part of the Perlmonk community as I find everyone on this sight extremely helpful and has helped me immensely. Thanks, Catfish	[reply]
Re^3: ChessBoard Program by LanX (Saint) on Feb 12, 2020 at 22:06 UTC
Syntax errors (almost) always force an abort of compilation. Always test your code with `perl -c your_file.pl` after typing a new line and you'll catch most typos. Or try the Komodo IDE it'll run the compilation automatically in the background and highlight broken code. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply] [d/l]

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