How to check user input data using letters

I am trying to create a function that asks a user to enter a capital letter A through J. if the letter is lowercase or from K-Z, I need to prompt the user to enter a valid letter. My code so far

function HumanInputFxn(Letter_Input)
Good=0;%initilizes loop variable 
while Good<1
    Letter_Input=input('Enter capital letter from A to J:'); %allows user to enter a letter
    if Letter_Input = num2cell('a':'z') || Letter_Input = num2cell('K':'Z')
        %a lower case letter or uppercase letter above J
        fprintf('you entered %c \n please enter a capital, valid letter. \n',Letter_Input);
    else %if the input is a valid
        fprintf('You have entered %c, a valid letter! You will now be prompted to enter a number.\n',Letter_Input)
        Good=1; %stops letter loop
    end
end
end

I get errors the following errors:

Unrecognized function or variable 'Letter_Input'.

Error in HumanInputFxn(Letter_Input)

Incorrect use of '=' operator. To assign a value to a variable,

use '='. To compare values for equality, use '=='.

How can I properly define invalid inputs in my if statement? Why is Letter_Input not recognized? thanks

Answer 1

[Sudhakar Shinde]

you could try this:

function HumanInputFxn(~)
Good=0;%initilizes loop variable 
while Good<1
    Letter_Input=input('Enter capital letter from A to J: ','s'); %allows user to enter a letter
    if any(contains(num2cell('a':'z'),Letter_Input)) || any(contains(num2cell('K':'Z'),Letter_Input))
        %a lower case letter or uppercase letter above J
        fprintf('you entered %c \n please enter a capital, valid letter. \n',Letter_Input);
    else %if the input is a valid
        fprintf('You have entered %c, a valid letter! You will now be prompted to enter a number.\n',Letter_Input)
        Good=1; %stops letter loop
    end
end
end

[scobug411]

this worked, thank you!!

[Adam Danz]

try these inputs,

• 'ABC'
• 1

[Sudhakar Shinde]

Welcome.

Answer 2

[Adam Danz]

The input() method of acquiring responses from a user is highly unconstrained and difficult to manage (see this example). What if the user enters more than 1 letter? or a number or a punctuation character? I suggest using a question dialog box or some other constrained user interface.

Nevertheless, here are two tests that are fairly leak-proof to confirm that,

• The user entered 1 and only 1 character
• The input is a character or string
• The character was between A and J
• The character was upper case

Good = false; % initilizes loop variable
while ~Good
    Letter_Input=input('Enter capital letter from A to J:','s'); % allows user to enter a letter
    isValid = sum(ismember('A':'J',char(upper(Letter_Input))))==1 ...
        && (ischar(Letter_Input) || isstring(Letter_Input)); % test for A:J (ignores case)
    caseIsValid = isstrprop(Letter_Input, 'upper'); % tests for case
         
    if ~isValid || ~caseIsValid
        %a lower case letter or uppercase letter above J
        fprintf('you entered %c \n please enter a capital, valid letter. \n',Letter_Input);
    else
        fprintf('You have entered %c, a valid letter! You will now be prompted to enter a number.\n',Letter_Input)
        Good=1; %stops letter loop
    end
end