How can i keep repeating the question until they the user makes the correct input?

So I created a code that takes in 3 inputs from the user, being "start", "increment" and "stop". The code basically prompts the user to input these numbers through a dialog box. However, I realised that there were problems with the code such as the user making the input for start bigger than the input for stop. I did try to fix this but it ended up causing a broken infinite loop that couldn't be stopped unless Task Manager was whipped out to take it out of its misery.

The code:

%User input for start and stop times
s = 1;
prompt = {'Enter Start time:','Enter increment:','Enter Stop time:'};
title = 'Input';
dims = [1, 35];
answer = inputdlg(prompt,title, dims)
start = str2num(answer{1})
increment = str2num(answer{2})
stop = str2num(answer{3})



if start > stop
    while s == 1
        error = msgbox('ERROR: Start cannot be larger than Stop time. Try again')
        uiwait(error)
        disp('Program execution resumed')
        answer = inputdlg(prompt,title, dims)
        s = 0
    end
else
    disp('This is legal')
    s = 1;
end

I only intended the loop to keep prompting the user to put in an appropriate input until that requirement was met.

Answer 1

[Asad (Mehrzad) Khoddam]

The start and stop should be defined in the loop as well

%User input for start and stop times
s = 1;
prompt = {'Enter Start time:','Enter increment:','Enter Stop time:'};
title = 'Input';
dims = [1, 35];
answer = inputdlg(prompt,title, dims)
start = str2num(answer{1})
increment = str2num(answer{2})
stop = str2num(answer{3})



while start > stop
    error = msgbox('ERROR: Start cannot be larger than Stop time. Try again')
    uiwait(error)
    disp('Program execution resumed')
    answer = inputdlg(prompt,title, dims)
    start = str2num(answer{1})
    increment = str2num(answer{2})
    stop = str2num(answer{3})        
end
disp('This is legal')