How to write a function to determine if the inputed date is valid.Whats wrong with my valid_date function?

function valid = valid_date(year,month,day)

if isscalar(year)==true && year>0 && isscalar(month)==true && month>0 && 12>=month && isscalar(day)==true && day>0 %checks if input is correct
    
    if (mod(year,4) == 0 && mod(year, 100)~= 0 || mod(year,400)==0) %checks if it's leap 
    isleap=true;
    else
    isleap=false;
    end

    if( any(month == [4,6,9,11]) && day<=30 )
        valid = true;
        if ( any(month == [1,3,5,7,8,10,12]) && day<=31)
            valid = true;
        else
           valid=false;
        end
    end
    elseif isleap == true && month == 2 && day<=29 || isleap == false && month ==2 && day<=28
      valid=true;
    else
     valid=false;
    end
else
    valid=false;
end
    
end

Answer 1

[James Tursa]

Consider these lines:

    if( any(month == [4,6,9,11]) && day<=30 )  % <-- if you pass this test
        valid = true;
        if ( any(month == [1,3,5,7,8,10,12]) && day<=31) % <-- then how could you ever pass this test

That is, if the month is one of [4,6,9,11] and you passed that first if-test, then how can you ever pass that 2nd if-test which is inside the if-block of the first test? (You can't)

You need to rethink and rework this logic. Step through it one line at a time to see what it is really doing with those incorrect results.

[anika kader]

this didnt work.

[anika kader]

[James Tursa]

Do you know how to use the debugger? Bring your code up in the editor, then click on a line number, e.g. near the start. When you run your code, it will pause at the line number. Then you can click one of the buttons at the top to step through your code one line at a time. Do this for one of your failed results and then you can see what the code is acutally doing so you can see the flaws in the logic.

[anika kader]

thank u so much..it worked