if (~(isstrprop(blockVal,'digit'))) || (str2num(blockVal) < 0) || ...
        (str2num(blockVal) > 9) || (isinteger(str2num(blockVal)))
    % Error about one digit numerics only
    errordlg('Block entries must be limited to the integers 0 to 9.  0 denotes any number possible.'...
        ,'One Digit Numeric Integers Only');
else
    puzzle(1,1).block = blockVal;
end