function s = e11v4(m)
% s = e11v4(m): return a $m$-by-$2m$ string matrix $s$ with
% + $*$s on the border (left, right, top, and bottom edges)
% + $\$s on the diagonal, except for on the border
%   (the *diagonal* of a matrix = all valid positions (i,i) in the matrix)
% + $-$s below the diagonal, except for on the border
% + $+$s on the boundary, $@$s in the interior, and $c$ at the center of
%   a disk of radius $round(m*.35)$ and center $(round(m*1.5),round(m/2))$

% version where we loop over all positions and test a condition to see
%               if we care about that position

n = 2*m; % width of $s$             % [3/14] fixed typo below, where $xc<-->yc$
xc = round(m*1.5); yc = round(m/2); % (yc,xc) = center of disk
r = round(m*.35);                   % radius of disk

% note: deleted definition of coordinate matrices $x$,$y$ from skeleton code

s(m,n) = ' '; % make $s$ large enough
s(:,:) = 'o'; % fill each element with $'o'$

% place $-$s below diagonal: y > x
    for y = 1:m
        for x = 1:n
            if y > x
                s(y,x) = '-';
            end
        end
    end

% place $\$s on diagonal: y = x
    for y = 1:m
        for x = 1:n
            if y == x
                s(y,x) = '\';
            end
        end
    end
    

% place $*$s on border: x = 1, x = n, y = 1, y = m
    for y = 1:m
        for x = 1:n
            if x == 1 | x == n | y == 1 | y == m
                s(y,x) = '*';
            end
        end
    end


% place $@$s inside disk: d < r
    for y = 1:m
        for x = 1:n
            d = sqrt((x-xc)^2 + (y-yc)^2);
            if d < r
                s(y,x) = '@';
            end
        end
    end
    

% place $+$s on disk: r - .5 < d < r + .5
    for y = 1:m
        for x = 1:n
            d = sqrt((x-xc)^2 + (y-yc)^2);
            if r - .5 < d & d < r + .5
                s(y,x) = '+';
            end
        end
    end

% place $c$ at center of disk (done for you:)
    s(yc, xc) = 'c';