The lines inside my while-loop are never executed

function lagre(filename)

res = 1;
fid = fopen(filename,'w');

while (res ~= [])
    res = input('Type in text that you want to save, and press Enter. Leave a blank space and press Enter to quit.');
    fprintf(fid, '%s \n', res);
end

fclose(fid);

end

The lines inside this while-loop are never executed, and I don't understand why. 1 is certainly unequal to nothing, right?

Answer 1

[dpb]

...1 is certainly unequal to nothing, right?

Yabbut... :)

The ~= comparison fails because the two results are incompatible in type/class.

Use

while ~isempty(res)

instead.

[Guillaume]

To add to that, matlab has many different ways to arrive at the empty set, none of which it considers equal with isequal. With == you have the additional problem that these empty have different sizes (sic!)

a = 1;
a(1) = []; % a is now empty
isequal(a, []) %return false!
isequal(a, double.empty(0,1)) %return false!
a == [] %error dimension not equal

Always use isempty to test for emptiness.