Frustrating for what should be simple… What have I done wrong?

Here is an example of some simple code I have written. When I ask the user for a yes/no answer it works for yes but gives an error when they enter no (matrix dimensions do not agree). However it does work if the input is only a y or n. Why is this?

a = 'no';

while a ~= 'yes'

    a = input('Do you like the colour red? (yes/no) ——>  ','s');
if a == 'yes'
    disp('Good its the best colour ever')
elseif a == 'no'
    disp('Whats wrong with you?... TRY AGAIN')
else
    disp('Thats not an answer, enter y for yes or n for no.')
end

end

THANKS!!

Answer 1

[Paul]

For strings you shouldn't use == to compare but strcmp for case sensitive comparison or strcmpi for not case sensitive. So this code should work for you:

a = 'no';

while ~strcmpi(a,'yes')
    a = input('Do you like the colour red? (yes/no) ——>  ','s');
    if strcmpi(a,'yes')
        disp('Good its the best colour ever')
    elseif strcmpi(a,'no')
        disp('Whats wrong with you?... TRY AGAIN')
    else
        disp('Thats not an answer, enter y for yes or n for no.')
    end
end

[Jack]

THANKS!!

Answer 2

[Azzi Abdelmalek]

Use

while ~isequal(a,'yes')

You can't compare 'yes' and 'no' using ==, try this

'abc'=='abf'

the result is a comparison character by character. The two strin must have the same number of characters

1 1 0

because the first two element are the same, but not the third. Now if you use

isequal('abc','abf')

the result is

0

because isequal compare the two string, there is no comparison character by character.

Answer 3

[Jos (10584)]

Another option with strings is to use SWITCH-CASE-END in combination with a WHILE-loop and a BREAK statement. The big advantage using SWITCH over IF is that you can accept different answers

while (1)
    a = input('Do you like the colour red? (yes/no) ——>  ','s');
    switch lower(a)
    case {'yes','y','jawohl','yes sir yes','yes i do'}
       disp('Good, it''s the best colour ever') % note the double quotes ...
       break ; % Breaks out of the infinite while loop
    case {'no','n','nope','no way man!','njet','i hate red'}
       disp('What''s wrong with you?... TRY AGAIN') 
    otherwise
       disp('That''s not an answer, enter y for yes or n for no.')
    end
end

(Edited…Thanks Paul!)

[Paul]

I think you mean switch instead of which.

[Jos (10584)]

Of course! ;-) Sorry.