How can I create a function that gives me logical true or logical false for a certain date?

I've been doing a Coursera course for MatLab and I'm stuck in this task that ask me for this function. Debugger have helped but I'm not been able to find any more mistakes

This is my code so far:

function [valid] = valid_date(year, month, day)
%rule for non scalar inputs
    if ~isscalar(year) == true || ~isscalar(month) == true || ~isscalar(day) == true
        valid = false;
    else 
        valid = true;
        return
    end
%rule for other months
M31 = [1 3 5 7 8 10 12];
    if ismember(day, 1:31) == 1  
    elseif ismember(month, M31)
        valid = true;    
    else 
        valid = false;
    end
    if ismember(day, 1:30) == 1
M30 = [4 6 9 11]
    elseif ismember(month, M30)
        valid = true;
    else
        valid = false;
        return
    end
%rule for february
    if month == 2
    elseif ismember(day, 1:28) == 1
        valid = true;
    else 
        valid = false;
    end
%rule for non-leap years
    if month == 2 && day == 29
    elseif mod(year, 4) ~= 0 
    end
        valid = false;
%rule for leap years
    if mod(year, 400) == 0
        valid = true;
    elseif mod(year, 100) == 0
        valid = false;
    elseif mod(year, 4) == 0
        valid = true;
    else
        valid = false;
    end
end

[Geoff Hayes]

Vinicius - this first block seems a little overly complex

    if ~isscalar(year) == true || ~isscalar(month) == true || ~isscalar(day) == true
        valid = false;
    else 
        valid = true;
        return
    end

If you are exiting the function early then valid should be false. I think that you could instead have

    valid = true;
    if ~isscalar(year) || ~isscalar(month) || ~isscalar(day)
        valid = false;
        return;
    end

As for any other bugs, are there specific inputs that return an invalid response?

[Vinícius Nogueira Freitas Silveira]

Yes, dates of random non-leap years like (1995, 2, 29) and random dates like (223, 12, 32).

[Geoff Hayes]

I recommend that you put a breakpoint in your code and use the MATLAB debugger to step through each line. See what happens to valid when the year is 1995, the month is 2, and the day is 29. If your above code is not returning the correct response (false), then there must be some line that is setting valid to true...the debugger should help you determine that.

Answer 1

[Walter Roberson]

    if ~isscalar(year) == true || ~isscalar(month) == true || ~isscalar(day) == true
        valid = false;
    else 
        valid = true;
        return
    end

If any of year, month, or day are not scalar, then you set valid = false but you continue execution even though it is not possible for the date to be later determined to be valid under those circumstances.

If all of year, month, and day are scalar, then you set valid = true and return without having processed any of the other tests, so you would for example declare that year -17 month 42 day 3.8 is acceptable input.

[Vinícius Nogueira Freitas Silveira]

Should I create a general rule, for example, using the fix, ceil, floor or round functions, to exclude those imputs?