with TEXT_IO; 
package INTEGER_IO is new TEXT_IO.INTEGER_IO(INTEGER);
with TEXT_IO, INTEGER_IO;
use TEXT_IO, INTEGER_IO;

procedure Queens is

BSize : INTEGER := 0;
procedure Title is
begin
   NEW_LINE;
   PUT_LINE("######  ##  ##  ######  ######  ##    ##  ######");
   PUT_LINE("######  ##  ##  ######  ######  ###   ##  ######");
   PUT_LINE("##  ##  ##  ##  ##      ##      ####  ##  ##    ");
   PUT_LINE("##  ##  ##  ##  ######  ######  ##### ##  ######");
   PUT_LINE("##  ##  ##  ##  ##      ##      ## #####      ##");
   PUT_LINE("### ### ######  ######  ######  ##  ####  ######");
   PUT_LINE("#### ## ######  ######  ######  ##    ##  ######");
   NEW_LINE(3);
end title;

procedure GetBSize(Size : out INTEGER) is
Temp : INTEGER := 0;
begin
   While Temp<1 loop
      PUT("What is the size of the chess board?");
      GET(Temp); NEW_LINE;
      if Temp<1 then 
         PUT_LINE("Positive integers only please.");
      end if;
   end loop;
   Size := Temp;
   exception when others =>
         PUT_LINE("Erroneous input - Board size will be 8.");
         Size := 8;
end GetBSize;

procedure DoQueens(Size : in INTEGER) is

subtype BType is INTEGER range 1..Size;
type BArray is array (INTEGER range 1..Size) of BType;
Board : BArray;
Fail : BOOLEAN;

   procedure DrawBoard(Rows : in INTEGER;
                       Board : in BArray) is
   R, C : INTEGER;
   begin
   for R in 1..Rows loop
      for C in 1..Rows loop
         if (Board(R) = C) then PUT("Q ");
         else PUT("+ ");
         end if;
      end loop;
      NEW_LINE;
   end loop;
   end DrawBoard;

   function Place( Size, Row : INTEGER)
		   return BOOLEAN is

   IsGood : BOOLEAN := False;
   Column : INTEGER := 0;
   Left, Right : INTEGER;
   Void : BOOLEAN;

   begin
   if Row>Size then return TRUE; end if;
   while not (Row=1 and Column>Size) loop
      while not IsGood loop 
         IsGood := TRUE;
    	 Column := Column + 1;
	 Left := Column;
	 Right := Column;
         for N in reverse 1..(Row-1) loop
            Left := Left - 1;
	    Right := Right + 1;
            if Left>0 then 
              if Board(N)=Left then IsGood := FALSE;
 	    end if; end if;
	    if Right<=Size then 
	      if Board(N)=Right then IsGood := FALSE;
	    end if; end if;
            if Board(N)=Column then IsGood := FALSE; end if;
         end loop;          
 	 if Column=Size and IsGood=FALSE then return FALSE; end if;
      end loop;
      
      Board(Row) := Column;
      if place(Size, Row + 1) then return TRUE; end if;
      if Column<Size then Column := Column + 1;
      else return false; end if;
   end loop;
      return FALSE;
   end Place;

begin
   if Place(Size, 1) then DrawBoard(Size, Board); 
   else PUT_LINE("No solution possible");
   end if;
end DoQueens;

begin
   Title;
   GetBSize(BSize);
   DoQueens(BSize);
end queens;