how to "convert" user inputted letter and number combination to a row,col position on a plot?

I am trying to program a game of Battleship, where a human plays against a computer. The user is to input a number, for example 'A', and a number, for example, '7'. I have already plotted the positions of both the human and computer ships. How do I correspond the user input A7 to a position on the plot, for example row=1, col=7? Also, how can I randomly determine a letter-number combo for the computer and correspond it to a row,col position? These should both loop until either the player or computer hits all ships

thanks

Answer 1

[Adam Danz]

"The user is to input a number..."

How is the user providing these inputs? If you're using the input() function, don't. It's highly unconstrined allowing the user to enter virtually anything (more info: link1, link2).

"How do I correspond the user input A7 to a position on the plot, for example row=1, col=7?"

The numeric part already corresponds to the column number. To convert the letter A:Z to row numbers,

% letter is a single character A:Z (or a:z).
% char() is there in case user enter a string "A" intead of a char 'A'
letter = 'B';
rowNumber = double(upper(char(letter)))-64

rowNumber = 2

"how can I randomly determine a letter-number combo for the computer and correspond it to a row,col position"

M is the size of your matrix.

n is the number of random samples you want

M = ones(15,20);  
n = 5; 

randLetters = char(randi([65, size(M,1)+64],n,1))

randLetters = 5x1 char array
    'G'
    'H'
    'I'
    'L'
    'E'

randNumbers = randi([1,size(M,2)],n,1)

randNumbers = 5×1

15 18 15 20 9

●

If you want to combine the letters and numbers, into the form 'A1', the numbers need to be converted to characters.

LN = strcat(randLetters, compose('%d',randNumbers))

LN = 5x1 cell array
    {'G15'}
    {'H18'}
    {'I15'}
    {'L20'}
    {'E9' }

Answer 2

[Ameer Hamza]

For case when you have a string like 'A7'

str = 'A7';
nums = str - ('A1'-1);

Result

>> nums
nums =
     1     7

For randomly generating such a string

str = char([randi([65 97]) randi([48 57])]); % ascii ranges of alpha numeric values

Result

>> str
str =
    'I6'

Answer 3

[J. Alex Lee]

In case you want to make battlship on an insanely large grid, here's a more general solution to convert "Excel column" style labels into a number (case insensitive), assuming character arrays and cellstr's (strings not supported, but i think pretty simple to extend)

function d = alpha2dec(s)
% convert A-Z to 1-26, AA=27, AB=28, etc.
%
% d = alpha2dec(s) 
% 
% returns the decimal d of string s which represents d in base 26
% expressed as 'A'..'Z', 'AA','AB'...'AZ'
%
% Examples
%   alpha2dec('A')   returns 1
%   alpha2dec('Z')   returns 26
%   alpha2dec('IV')  returns 256
%   alpha2dec('esa') returns 3875
%
% notes:
% 1. In ASCII, 'a' does not equal 'A', so we ensure the conversion works by
%    transforming s to upper
%

if ~iscell(s)
	s = {s};
end

d = nan(size(s));

for j = 1:length(s)
	
	n = length(s{j});               % number of letters in the string
	p = 26.^((n-1):-1:0);        % powers of the base
	a = upper(s{j}).' - 'A' + 1;    % convert each "digit" into integer 1-26
	
	d(j) = p * a;                   % output is the power series in b26
end

end % alpha2dec