How to use not equal to '~=' operator in if statement?

My code works fine with '==' but not with '~='.I expect it not to display 'error' if user enters A or B

    x=input('input x','s')
    if(x~='A')||(x~='B')
        disp('error');
    end

Answer 1

[John D'Errico]

A problem of elementary logic?

You want an error to return only if A is not in the set {'A','B'}. So a call to ismember might be a good alternative.

Regardless, given the approach you have followed, if x is equal to 'A', then the second half of the clause will be true, even though the first part of the clause is false. And the logical statement

   false || true

is TRUE.

You are asking for a result that is only true when BOTH parts of the clause are true. Use a logical and, NOT a logical or.

if(x~='A') && (x~='B')

Answer 2

[Jan]

Remember, that the negation of

(x=='A') || (x=='B')

is:

~((x == 'A') ||  (x == 'B'))   ==>
 ~(x == 'A') && ~(x == 'B')    ==>
  (x ~= 'A') &&  (x ~= 'B')

[Zhuoying Lin]

Hi I have a similar question:

when I type:

if (x ~= 'a') && (x ~= 'p') && (x ~= 'T')

       fprintf('ERROR:You entered incorrect choice.')

end

but it also shows that:

Operands to the || and && operators must be convertible to
logical scalar values.

Error in term (line 4)
if (x ~= 'a') && (x ~= 'p') && (x ~= 'T')

[Walter Roberson]

if any((x ~= 'a') & (x ~= 'p') & (x ~= 'T'))
       fprintf('ERROR:You entered incorrect choice.')
end

or

if ~all( ismember(x, {'a', 'p', 'T'}) )
  fprintf('ERROR:You entered incorrect choice.')
end

Answer 3

[Torsten]

If user enters A, then x~=B is true, so (x~='A')||(x~='B') is true, thus "error" is displayed.

Same for B.

Best wishes

Torsten.