How to set BackgroundColor on edit text using mycode and fix 1 error?

function [] = main ()
figure('name','CROSSWORD PUZZLE','MenuBar','none','Color',[.7,.78,1],'units','normalized','outerposition',[0 0 .5 .8]')
Title='CROSSWORD';
a=1;
for x=20:30:260
    tagn=strcat('TBox',num2str(a));
    uicontrol('Style','edit','position',[x, 530, 30, 30],'String',Title(a),'FontSize',20,'Tag',tagn)
    a=a+1;
end
TitleB='PUZZLE';
a=1;
for x=80:30:230
    tagn=strcat('TBox1',num2str(a));
    uicontrol('Style','edit','position',[x, 500, 30, 30],'String',TitleB(a),'FontSize',20,'Tag',tagn)
    a=a+1;
end
S.pb = uicontrol('Style','pushbutton','Position',[500 350 60 30],'String','PLAY');
set(S.pb,'callback',@game)
S.ob = uicontrol('Style','pushbutton','Position',[500 300 60 30],'String','OPTION');
set(S.ob,'callback',@set)

function [] = game(hObject, eventdata, handles)
 set(hObject,'Visible','off');
[numeric,strings]=xlsread('puz.xlsx', 'sheet1', 'A1:N14');
a=1;
for x=20:30:620
    for y=420:-30:30   
         Ebox(a)=uicontrol('Style','edit','position',[x y 30 30],'FontSize',20,'String',strings(a))
         if string(a)==''
             set(Ebox(a),'BackgroundColor','black')
         end
        a=a+1;
    end
end

Answer 1

[Walter Roberson]

You do not define "string". You do define "strings", but that output from xlsread() would be a cell array of strings so you would need {} indexing to access it:

if isempty(strings(a))  %(if you are checking for empty entry)

or

if strcmp(strings(a), ' ')  %(if you are checking for blank)