how do you check that a value input into your code is exactly 7 digits long before proceeding?

in my code we enter a value that is seven digits long our school id's for example

idNumber = ('1234567');

how can i verify that this number is seven digits long using a loop?

[per isakson]

Why not

>> idNumber = ('1234567');
>> length(strtrim(idNumber))
ans =
     7
>> 

Answer 1

[Stephen23]

idNumber = '1234567';
assert(numel(idNumber)==7,'Wrong length ID number')