MATLAB: Matrix and element change and input help

Question

This may be trivial but how do I get for a user input coords as a matrix, and to change the element to another number eg. a tic-tac-toe game player 1 inputs a coord to change a 0 in the matrix to a 1, and player 2 changes a 0 to -1. (player==0 when it is player 1's turn)

my code:

        I=input('Number coordinate: ');
        for a=1:3
           for b=1:3
               if B(a,b)==0
                   if I==1
                       if player==0
                           B(1,1)=1;
                       else
                           B(1,1)=-1;
                       end
                   elseif I==2
                       if player==0
                           B(1,2)=1;
                       else
                           B(1,2)=-1;
                       end
                   elseif I==3
                         if player==0
                           B(1,3)=1;
                       else
                           B(1,3)=-1;
                         end
                   elseif I==4
                         if player==0
                           B(2,1)=1;
                       else
                           B(2,1)=-1;
                         end
                   elseif I==5
                         if player==0
                           B(2,2)=1;
                         else
                           B(2,2)=-1;
                         end
                   elseif I==6
                         if player==0
                           B(2,3)=1;
                       else
                           B(2,3)=-1;
                         end
                   elseif I==7
                         if player==0
                           B(3,1)=1;
                       else
                           B(3,1)=-1;
                         end
                   elseif I==8
                         if player==0
                           B(3,2)=1;
                         else
                           B(3,2)=-1;
                         end
                   elseif I==9
                         if player==0
                           B(3,3)=1;
                         else
                           B(3,3)=-1;
                         end
                   end
               else
                   disp('That is an invalid move')
               end
           end
        end

problems with it: It will let a user set a piece on an already used part of a matrix and will always say that it is an invalid move (even if it is valid)

Could anyone help me to find a good way to do this?

-thanks, Alex

Answer 1

I think you are trying to do just this:

BB = reshape(B',9,1);
I=input('number coord:');
player = 1;
BB(I) = 2*(player == 0) - 1; 
B = reshape(BB,3,3)';

aren't you?