Im designing a game of battleship, but. im trying to use a code to prevent the user from placing a ship out of bounds

in my game of battleship the board is 6 by 6, so when the user wants to place a (1X2) ship on grid 6 and chooses a horizontal orientation the ship will be placed out of bounds. My code for just placing the ships is:

startingGrid= input(' Please choose the grid number you want your ship to start in : ');

if startingGrid == 1
    while true
        orientation = input(' Please enter v if you want your ship to be placed vertically or h if you want it horizontally', 's');
        if ismember(orientation,{'v' 'h'})
            break;
        end
        disp(' please choose v or h only and make sure to use small letters ');
    end
if strcmp(orientation,'v')
% fill grids 1 and 7
else
%fill grids 1 and 2
end

and i have an if statement like this for each of the 36 "starting grids".

I also wrote this code to not allow a ship to be placed out of bounds,( for example starting grid of 6 and orientation of h.

validChoice = false; % set flag up front, false so we enter the loop at least once
while ~validChoice
    startingGrid= input('Enter top-left grid square number','s');
    startingGrid = str2double( startingGrid );
    orientation = input('Enter v or h for vertical or horizontal','s');

    if (startingGrid==6 && strcmpi(orientation,'h'))
        % This is invalid
        disp( 'Invalid choice, cannot fit ship in chosen location, try again...' );
    else
        % Input is OK, set the flag to true so the loop exits
        validChoice = true; 
    end
end

now is there a way to somehow use this code inside my if statement, so

if startingGrid ==6 
.......

if v 
%fill grids 6 and 12
else 
%use above code to let the user enter a starting grid again.
end

[Meg Noah]

Editing and reposted as answer below.

[Tariq Hammoudeh]

thank you for that, but i already have code for the board, and the ability to place ships on the board, its just that i do this for each grid individually using the if statements in my question. All i need is a way to allow the user to enter a different startingGrid when his choices would place the ship out of bounds. And again because i am doing this individually, so:

if startingGrid ==1
    ......
        
elseif startingGrid ==2
    ....
        
elseif StartingGrid ==3
    .
    .
    .
    .

I just need code to put in:

if startingGrid == 6
    while true
        orientation = input(' Please enter v if you want your ship to be placed vertically or h if you want it horizontally', 's');
        if ismember(orientation,{'v' 'h'})
            break;
        end
        disp(' please choose v or h only and make sure to use small letters ');
    end
if strcmp(orientation,'v')
% fill grids 6 and 12 (I already have code for this)
else
%code to display "ship will be out of bounds" and allows the user to enter a startingGrid again
end

and ill just put this code in each scenario where the ship will be out of bounds.

[Meg Noah]

Just have a while loop for the query and break if they input a valid location.

[Tariq Hammoudeh]

i tried something like that, but then it doesnt process the input again, as in check if startingGrid == 1 and so on, so is there a way i can make that work

Answer 1

[DGM]

I generally can't stand things written to be so tediously interactive like this, but maybe this is a simplified start.

% i assume you have some sort of equivalent variables defined
shipsize = 2;
boardsize = [6 6];
N = prod(boardsize);

board = false(boardsize); % assuming the board is empty at this point

% get valid placement information from user
while true
    shiplocation = requestshiplocation(N);
    orientation = requestorientation();
    
    [m n] = ind2sub(boardsize,shiplocation);
    if strcmp(orientation,'v') && m + (shipsize-1) > boardsize(1)
        fprintf(' Ship can''t fit this close to the bottom edge of the board in this orientation\n')
    elseif strcmp(orientation,'h') && n + (shipsize-1) > boardsize(2)
        fprintf(' Ship can''t fit this close to the right edge of the board in this orientation\n')
    else
        break;
    end
end

% place this ship on the board
if strcmp(orientation,'v')
    board(m:m+shipsize-1,n) = true;
else
    board(m,n:n+shipsize-1) = true;
end
board

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function shiplocation = requestshiplocation(N)
    while true
        shiplocation = input(sprintf('Specify where this ship is located (grid position between 1 and %d): ',N));
        if isscalar(shiplocation) && (shiplocation >= 1 && shiplocation <= N)
            break;
        end
        fprintf(' please choose a valid location between 1 and %d \n',N);
    end
end

function orientation = requestorientation()
    while true
        ostring = input('Specify ship orientation (''v'' or ''h''): ', 's');
        orientation = lower(ostring(1)); % ignore case, length
        if ismember(orientation,{'v' 'h'})
            break;
        end
        fprintf(' %s is not a valid orientation\n',ostring)
    end
end

Points to consider:

Given the convention of asking only for an index and (one of two) orientations, a ship can be placed at an index where neither orientation is valid. This is why I simply chose to reject both the location and orientation when either is invalid.

Asking the user for the ship location as a linear index is cumbersome and nonintuitive. The actual game uses row and column subscripts, so it would make more sense to at least use that convention. Doing so would also obviate the need to use ind2sub().

Nothing in this approach prevents ships from being placed on top of each other.

[Walter Roberson]

boards_folder = 'C:\Users\rhys\Documents\ENG1007\Assignment5\ComputerBoards';
assert(exist(boards_folder, 'dir'), 'Missing boards folder')
dinfo = dir( fullfile(boards_folder, '*.csv') );
numfile = length(dinfo);
random_board_number = randi(numfile);
fileinfo = dinfo(random_board_number);
board_filename = fullfile(fileinfo.folder, fileinfo.name);
assert(exist(board_filename, 'file'), 'Board file disappeared!')
board_data = readtable(board_filename);

%now use board_data to build the board.

[DGM]

What's that from? I'm missing context here.

Is there another thread about this assignment that I'm missing? I think I saw some others recently.

[Tariq Hammoudeh]

I asked 2 other questions, but arent related to the main functionality of the game

[Walter Roberson]

@Rhys Davies recently posted a Question about battleships that included a query about random boards. But unfortunately I trusted Rhys and so did not think to lock down the question, so they were able to delete the question and all of the work that the volunteers had put into it.

Then shortly before I posted the above comment, @Tariq Hammoudeh posted a Question about choosing a random board. I had trouble finding my previous response (because Rhys had deleted all my work :( :( ) but I managed to dig it out and post it in that Question. But I couldn't save my response bacause Tariq had deleted the question (before any posted responses though.) So I found an active Tariq discussion on the topic and copied in what I would have posted, so as not to lose it again.

[Tariq Hammoudeh]

my question is just about getting an error when using randsample() to get a random element of an array

[Walter Roberson]

You do not need to use randsample(). You can find the number of files, and use randi() on the number of files.

Unless, that is, you have a reason to pick between the files with different probabilities. If you wanted, for example, that one particular special board should show up 10 times its normal probability, then randsample() makes that slightly easier to code than using randi() [but it isn't difficult to arrange with randi either]

[Tariq Hammoudeh]

I just put the names of the files in an array and now i just want to select a random element of this array. so

A=random element of array

Then Ill use

if A= file1

......

So i just need to be able to pick a random element from my array

Answer 2

[Meg Noah]

Here is a solution with user interaction/prompting:

flagInteractive = 1; % prompt user for ship placement
flagRepeatable = 0;

if (~flagInteractive && flagRepeatable)
    iseed = 24;  % change this to get a different random outcome
    s = RandStream('mt19937ar','Seed',iseed);
    RandStream.setGlobalStream(s)
end

% index, name, size
% one for each ship to be placed (multiple ships of same type/length are
% uniquely included
Ships = {
    1,'Carrier',5; ...
    2,'Battleship',4; ...
    3,'Cruiser',3; ...
    4,'PatrolBoat1',2; ...
    5,'PatrolBoat2',2};
shipTable = cell2table(Ships,'VariableNames',{'idx','shipName','shipLength'});
nShip = numel(shipTable.idx);
shipTable.flagV = nan(nShip,1); % orientation of the ships (1=vertical, 0=horizontal)
% starting row and column of the ship on the gameboard
shipTable.iRow = nan(nShip,1);
shipTable.iCol = nan(nShip,1);

% board size
nrows = 10;
ncols = 10;

% create a board table
% empty values are 0
% filled values have shipIndex where the player has placed a ship
imBoard = zeros(nrows,ncols);
% row column indices for each tile
[C2X,R2X] = meshgrid(1:ncols,1:nrows);

for iShip = 1:nShip
    
fprintf(1,'\n\Current Gameboard\n');
for irow = 1:nrows
    for icol = 1:ncols
        if (imBoard(irow,icol) == 0)
            fprintf(1,'R%2.2dC%2.2d ',irow,icol);
        else
            % not allowed
            fprintf(1,'--%2.2d-- ',imBoard(irow,icol));
        end
    end
    fprintf(1,'\n');
end
    
    
    % prompt user for vertical or horizontal placement
    if (~flagInteractive)
        shipTable.flagV(iShip) = randi(2,1)-1;
    else
        list = {'Horizontal','Vertical'};
        [indx,tf] = listdlg('ListString',list,'PromptString', ...
            horzcat('Orientation of ',shipTable.shipName{iShip}), ...
            'SelectionMode','single');
        shipTable.flagV(iShip) = indx - 1;
    end
    
    nTiles = shipTable.shipLength(iShip);
    maskV = vertcat(zeros(nTiles-1,1),ones(nTiles,1));
    maskH = horzcat(zeros(1,nTiles-1),ones(1,nTiles));
    
    
    
    if (shipTable.flagV(iShip) == 0)
        % find the horizontal locations allowed
        imAllowedLocations = ones(nrows,ncols);
        imAllowedLocations(imBoard > 0) = 0;
        imAllowedLocations = imerode(imAllowedLocations,maskH);
        imAllowedLocations(C2X > ncols - nTiles + 1) = 0;
    else
        % find the vertical locations allowed
        imAllowedLocations = ones(nrows,ncols);
        imAllowedLocations(imBoard > 0) = 0;
        imAllowedLocations = imerode(imAllowedLocations,maskV);
        imAllowedLocations(R2X > nrows - nTiles + 1) = 0;
    end
    
    fprintf(1,'\nallowed locations for %s\n',shipTable.shipName{iShip});
    list = {}; listRow = []; listCol = [];
    for irow = 1:nrows
        if (irow == 1)
            fprintf(1,'    ');
            for icol = 1:ncols
                fprintf(1,'C%2.2d ',icol);
            end
            fprintf(1,'\n');
        end
        fprintf(1,'R%2.2d ',irow);
        for icol = 1:ncols
            if (imAllowedLocations(irow,icol) == 1)
                fprintf(1,'( ) ');
                list = vertcat(list,sprintf('R%2.2dC%2.2d',irow,icol));
                listRow = vertcat(listRow,irow);
                listCol = vertcat(listCol,icol);
            else
                % not allowed
                fprintf(1,'XXX ');
            end
        end
        fprintf(1,'\n');
    end
    
    if (~flagInteractive)
        % prompt for irow, icol - this is a random draw so replace the next
        % three lines with your user interface - how you want to propmpt
        idxAllowed = find(imAllowedLocations > 0);
        idxChosen = idxAllowed(randi(numel(idxAllowed),1));
        [thisRow,thisCol] = ind2sub(size(imAllowedLocations),idxChosen);
    else
        [indx,tf] = listdlg('ListString',list, ...
            'PromptString',horzcat('Location of\n ',shipTable.shipName{iShip}), ...
            'SelectionMode','single');
        thisRow = listRow(indx);
        thisCol = listCol(indx);
    end
    
    % populate the ship table and the game board for this player.
    shipTable.iRow(iShip) = thisRow;
    shipTable.iCol(iShip) = thisCol;
    if (shipTable.flagV(iShip) == 0)
        imBoard(thisRow,thisCol:thisCol+nTiles-1) = iShip;
    else
        imBoard(thisRow:thisRow+nTiles-1,thisCol) = iShip;
    end
    
end

fprintf(1,'\n\nFinal Gameboard\n');
for irow = 1:nrows
    for icol = 1:ncols
        if (imBoard(irow,icol) == 0)
            fprintf(1,'R%2.2dC%2.2d ',irow,icol);
        else
            % not allowed
            fprintf(1,'--%2.2d-- ',imBoard(irow,icol));
        end
    end
    fprintf(1,'\n');
end