How can I rerun my code if my given statement is not followed by the user?

%% Initiation of Version 2
disp('Version 2')
% Prompt user to input value from given options
program_str = input('Please select a program to optimize (1-Art, 2-Science, 3-Engineering): ','s');
program_optimization = program_str - '0';
switch program_optimization
    case 1
        tuition_cost = art_tuition_cost;
        disp('Congratulations!!! You have saved enough for the arts program.')
    case 2
        tuition_cost = science_tuition_cost;
        disp('Unfortunately!!! You do not have enough saved for the science program.')
    case 3
        tuition_cost = engineering_tuition_cost;
        disp('Unfortunately!!! You do not have enough saved for the engineering program.')
    otherwise
        while program_optimization ~= 1 || program_optimization ~= 2 || program_optimization ~= 3
            disp('Incorrect input entered. Only (1 2 3) allowed. Try again!')
            program_str = input('Please select a program to optimize (1-Art, 2-Science, 3-Engineering): ','s');
            program_optimization = program_str - '0';
        end
        if savings(end) >= art_tuition_cost
            disp('Congratulations!!! You have saved enough for the arts program.')
        elseif program_optimization == 2
            disp('Unfortunately!!! You do not have enough saved for the science program.')
        elseif program_optimization == 3
            disp('Unfortunately!!! You do not have enough saved for the engineering program.')
        end
end

My issue starts from under "Version 2". Any help would really be appreciated. Thank you.

[Benjamin Thompson]

Do you mean asking the user for input again if they do not enter 1, 2, or 3?

[Shane Jacob]

Yes.

Answer 1

[Walter Roberson]

%% Initiation of Version 2
disp('Version ²')

while true
    % Prompt user to input value from given options
    program_str = input('Please select a program to optimize (1-Art, 2-Science, 3-Engineering): ','s');
    program_optimization = program_str - '0';
    switch program_optimization
        case 1
            tuition_cost = art_tuition_cost;
            disp('Congratulations!!! You have saved enough for the arts program.')
            break
        case 2
            tuition_cost = science_tuition_cost;
            disp('Unfortunately!!! You do not have enough saved for the science program.')
            break
        case 3
            tuition_cost = engineering_tuition_cost;
            disp('Unfortunately!!! You do not have enough saved for the engineering program.')
            break
        otherwise
            disp('Incorrect input entered. Only (1 2 3) allowed. Try again!')
            %do NOT break here
    end
end

[Shane Jacob]

Also, if you dont mind could you explain the changes or why you made those changes? It will come in handy later and I was breaking my head behind this issue before. Thank you once again! :)

[Walter Roberson]

It is a common programming pattern.

There are two common ways of handling errors when asking for input:

1. ask for the initial input; check it, and if it is not valid, display an error message, then go back and display the original input prompt again; Versus
2. ask for the initial input; check it and if if it is not valid, then go back to prompt again, but displaying a different prompt message than the original one

Either way, it is better to have the code only check the responses in one place, as otherwise there is the risk that if the behaviours were to change, that you might accidentally update the behaviour in only one of the places.

It is a common pattern to use:

1. start a loop
2. prompt for input
3. check the inputs; if they were invalid, complain
4. if they were valid, act on them and then leave the loop
5. end of loop

But it is also entirely valid to instead program

1. start a loop
2. prompt for input
3. check the inputs; if they were invalid complain
4. if they were valid, then leave the loop
5. end of loop
6. act on the inputs -- which at this point are known to be valid (unless something in the processing of the inputs marked that the user asked to quit or that the user ran out of chances)

That second form has the advantage that you can often write the prompt / validation into a function, something like

[program_str, userquit] = get_input_str({'1', '2', '3'}, 'Please select a program to optimize (1-Art, 2-Science, 3-Engineering):', 'Incorrect input entered. Only (1 2 3) allowed. Try again!');

and then your main code does not need to loop at all: the loop is all inside get_input_str (which, for clarity, is a function you would write.)

[Shane Jacob]

Oooh, that makes sense. Thank you very much! I really appreciate it.

Answer 2

[David Hill]

program_str ='a';
while ~ismember(program_str,'123');
   program_str = input('Please select a program to optimize (1-Art, 2-Science, 3-Engineering): ','s');
end

[Shane Jacob]

Thank you for the suggestion! The other answer worked for me. Appreciate your effort.