Problem with an if statement

I have this code:

orientation= input (' enter v or h')

if orientation == v

......

end

but whenever i run the code and enter v or h, I get an error saying

Unrecognized function or variable 'v'.

So does matlab not take inputs in letters or is there a way to make it work.

Answer 1

[Voss]

Use the optional second argument to the input() function, 's', which tells input() to return exactly what the user entered, without evaluating it. You'll also need to compare orientation to 'v' rather than v or you'll just get the same error on the next line (and use strcmp/strcmpi in case they entered more than one character or an empty string).

orientation= input (' enter v or h', 's')
if strcmp(orientation,'v')
    % do v stuff
else
    % do h stuff
end

[Tariq Hammoudeh]

Thank you, for that but i just ended up using

if orientation == 'v'

....

But i have another question related to this,

Im using

if orientation == 'v'

....

elseif orientation == 'h'

.....

else

disp('choose v or h only')

end

How can i make it so that if neither v nor h are entered it displays this message and allows the user to try again

[Voss]

orientation = '';
while ~ismember(orientation,{'v' 'h'})
    orientation = input(' enter v or h', 's');
    if strcmp(orientation,'v')
        % do v stuff
    elseif strcmp(orientation,'h')
        % do h stuff
    else
        disp('choose v or h only');
    end
end

Or:

while true
    orientation = input(' enter v or h', 's');
    if ismember(orientation,{'v' 'h'})
        break;
    end
    disp('choose v or h only');
end
if strcmp(orientation,'v')
    % do v stuff
else
    % do h stuff
end

[Tariq Hammoudeh]

ok just one more thing, I joined this with my code and now its like this:

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')

.....

else

.....

end

I have many of those if statements, and i need to be able to let the user enter another startingGrid if they chose a specific number then either v or h. So basically in the

% do v stuff

or

% do h stuff

i tried

startingGrid=input('please try again')

but whenever i enter a different number the program just ends.

please note those "specific numbers" are things that i have different code to detect, so i only need the program to continue when i "try again", this is the only issue

[Voss]

I would make the startingGrid input and the orientation input independent of each other. Something along the lines of this:

while true
    startingGrid = input(' Please choose the grid number you want your ship to start in : ');
    % validate startingGrid with your other code here
    if startingGrid >= 1 && startingGrid <= 10 % whatever your valid condition is
        break
    end
    disp('please try again');
end

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

then validate startingGrid and orientation together after that, i.e., check some condition(s) that depend(s) on both startingGrid and orientation, which is not possible to check until both have been input.

This way you only ever need one while loop for each input, rather than many.

You probably will want to wrap that whole thing in a while loop too, for the consistency check between startingGrid and orientation:

while true

    while true
        startingGrid = input(' Please choose the grid number you want your ship to start in : ');
        % validate startingGrid with your other code here
        if startingGrid >= 1 && startingGrid <= 10 % whatever your valid condition is
            break
        end
        disp('please try again');
    end
    
    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
    
    % check consistency between startingGrid and orientation
    % if valid, break
    % else, issue statment (and the big while loop continues)
    
end

[Tariq Hammoudeh]

Im sorry i realized i wasnt too clear, those 'specific numbers" are just grid numbers where if you choose v or h on them the ship will be placed out of bounds, so what my actual code is:

disp(' You will now place your corvette (1X2) ship')

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

% orientation= input(' Please enter v if you want your ship to be placed vertically or h if you want it horizontally', 's');

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')

...

else

...

end

elseif startingGrid == 2

.. repeat the same code above but do different v and h stuff..

elseif startingGrid == 3

.....

So what i need for example is when startingGrid == 6

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')

..

else

display ('ship will be out of bounds please try again') and let the user try again

end.

because here when its h and starting grid 6 the ship will be out of bounds

Note: Im very well aware this isnt the most convenient way as ill have a over a 100 if statements, and ill have to go through each one individually, but its the only way i can think of.

[Voss]

If you can think of a way to combine orientation, startingGrid, the size of the grid, and the size of the ship into one or a few conditions to check, you'll be much better off and have many fewer if statements. For example:

grid_size = 6;
ship_size = 2;
startingGrid = 5;
orientation = 'h';

if startingGrid+ship_size-1 > grid_size
    disp('that''s a problem');
else
    disp('that''s ok');
end

that's ok

grid_size = 6;
ship_size = 2;
startingGrid = 6;
orientation = 'h';

if startingGrid+ship_size-1 > grid_size
    disp('that''s a problem');
else
    disp('that''s ok');
end

that's a problem

grid_size = 6;
ship_size = 3;
startingGrid = 5;
orientation = 'h';

if startingGrid+ship_size-1 > grid_size
    disp('that''s a problem');
else
    disp('that''s ok');
end

that's a problem

[Tariq Hammoudeh]

@Benjamin Thank you but, if the user enters 7 and h, then the above code wont let him, even though it should, so is there a way to fix it.

I tried:

while orientation=='h' && startingGrid==6 || orientation=='h' && startingGrid==12 % and so on for all conditions that will result in out of bounds

disp('Your ship will be placed out of bounds ')

startingGrid=input('Enter a grid number you want your ship to start in again : ');

orientation=input('Please enter v if you want your ship to be placed vertically or h if you want it horizontally : ','s');

end

and it works, but then for the bigger ships this line would get tooo long, so is there a way to fix the previous code so i can use something like

while orientation =='h' && startingGrid+shipSize-1 > bs

...

end

instead of the very long line

[Voss]

I would do it something like this. It doesn't check that ships don't overlap with each other, but it does check that each ship is on the board completely. I believe it has the structure you are looking for.

This code uses a 6-by-6 board, and assumes the definition of startingGrid is as follows: startingGrid = 1, 2, 3, 4, 5, 6 corresponds to the top row of the board, 7 is second row, first column, etc. (which is implied by your code). (Because this indexing is the opposite of how MATLAB does linear indexing in 2d matrices, it is convenient to build the transpose of the user-specified board and then transpose it at the end to get the final result.)

grid_size = 6;
board = zeros(grid_size);
ship_sizes = [2 3 5];

for i = 1:numel(ship_sizes)
    
    while true

        while true
            startingGrid = input(' Please choose the grid number you want your ship to start in : ');
            % validate startingGrid with your other code here
            if startingGrid >= 1 && startingGrid <= grid_size^2
                break
            end
            disp('please try again');
        end
        
        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
        
        % check consistency between startingGrid and orientation
        n_max = grid_size-ship_sizes(i)+1;
        if strcmp(orientation,'h')
            if mod(startingGrid-1,grid_size)+1 > n_max
                disp('Your ship will be placed out of bounds (off the right side of the board)');
                continue
            end
            % if valid, place the ship ...
            board(startingGrid+(0:ship_sizes(i)-1)) = i;
        else
            if floor((startingGrid-1)/grid_size)+1 > n_max
                disp('Your ship will be placed out of bounds (off the bottom of the board)');
                continue
            end
            % if valid, place the ship ...
            board(startingGrid+grid_size*(0:ship_sizes(i)-1)) = i;
        end
        
        % ... and break
        break
        
    end
    
end

board = board.';

disp(board);

[Tariq Hammoudeh]

Thank you

[Tariq Hammoudeh]

@Benjamin Again thank you i added this to my other code and it works fine, but i just want to ask what does the for loop do, I understood everything else but i just want to know what does this for loop do.

[Voss]

The for loop is to loop over the different ships, asking the user for each ship's startingGrid and orientation and placing each ship on the board.