MATLAB: How to check user input data using letters

charactersselection statementsstrings

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

Best Answer

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
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