How can I overcome 'Error: Undefined function or variable 'k'.' to check for a valid input?

I'm trying to write a code that will not output any errors but will define the errors in itself. Say if someone enters test(spaghetti, meatballs) (or 15pies, @%FAd, anything that isn't a number) I want to be able to address the problem in the function. What happens is matlab detects the error, breaks the function, and outputs the error message. I've tried exist(), isscalar(), isnumeric(), isnan(), etc. What am I missing here?

Example code

Function product = test(x ,y)
     if exist(x) && exist(y)
         product = x * y
     else
         disp('Please enter numerical values')
     end
end

If someone enters test(spaghetti, meatballs) The output should say "Please enter numerical values." What it does say is: "Error: Undefined function or variable 'spaghetti'."

It works correctly if I enter test(6, 8) or even test(spaghetti, meatballs) if both terms are predefined as numbers.

Answer 1

[Star Strider]

The ischar function is probably what you want. I created a cell array and used cellfun here to demonstrate. You can test ‘x’ and ‘y’ separately with ischar.

Example:

cv = {rand, '15pies', randi(9), 'spaghetti', randn, '@%FAd'};
check = cellfun(@ischar, cv)

check =

    1×6 logical array

     0   1   0   1   0   1

[Lewis Wooler]

I can see where that could be useful but I'm still getting the same results

the code

function product = test(x ,y)
     if ischar('x') && ischar('y')
         product = x * y;
     else
         disp('Please enter numerical values')
     end
end

still result in

test(spaghetti,7)
Undefined function or variable 'spaghetti'

I think this might just be an issue with Matlab itself

[Star Strider]

You need to test to be certain it is not a character, so use the tilde (~) to logically negate the results. Also, single quotes create string or character variables, so eliminate the quotes as well:

if ~ischar(x) && ~ischar(y)

That should do what you want.

Also, you have to assign something to ‘spaghetti’ for it to work in your code:

spaghetti = 20;                     % Numeric Variable
spaghetti = 'pasta';                % Character Variable

You may also need to test for cells, tables, structures, and others if you expect they could be passed as variables. Otherwise, they would all throw errors and return control to your Command Window rather than continuing to execute your code.