There's a mistake in the 5th line of you code.You're using == .You need to use =.
Also,you need to have the first assignment to 'button' before comparing it in the while condition.The code below works fine.I just made a few modifications to your code:
london = datetime;
timeZones = {'Amsterdam', 'Tokyo', 'Canberra', 'Los Angeles', 'New York', 'Local (London)','Close'};
button = menu('Choose your timezones',timeZones);
while button~=7 %7th button is 'close'
%Amsterdam
if button ==1
ams=london+hours(1);
disp(ams);
disp('+1:00');
%Tokyo
elseif button ==2
tok=london+hours(9);
disp(tok);
disp('+9:00');
%Canberra
elseif button ==3
can= london +hours(11);
disp(can);
disp('+11:00');
%Los Angeles
elseif button==4
los = london +hours(-8);
disp(los);
disp('-8:00');
%New York
elseif button==5
new= london +hours(-5);
disp(new);
disp('-5:00');
%London(Local)
elseif button==6
disp('No time difference');
disp(london);
else
end
button = menu('Choose your timezones',timeZones);
end
