MATLAB: Find out if number is divisible by x

divisors

I'm trying to write a function that determines if the input is a valid date, and for that I need a function that will tell me if an input number is divisible by 4 and at the same time not divisible by 100 (this has to do with leap years but I'm not supposed to use the special function for that). This is what I came up with but I can already see that it's not correct. In non-code language, I would like it to be something like "If divisors(year) contains the number 4 and does not contain the number 100, display the following…" but I did not know how to do this.

(This is just the part of code I'm struggling with, I didn't paste everything because it was quite a lot.)

Any tips on how I should fix it would be much appreciated!

function valid = valid_date(year,month,day)
if divisors(year) = 4 ~ 100
    
.    
.    
.
.
.
end

Best Answer

Thank you for your help so far! So now I came up with this and it works with some dates but not with most; For example, I tried it with the input (2001,1,32) and it returns "1" although the input is not a correct date.

Also sometimes I'm getting the error message Output argument "valid" (and maybe others) not assigned during call to "valid_date".

I don't know what that message means and what else is wrong in my code, maybe someone can point out where the mistake is?


function valid = valid_date(year,month,day)
% leap year: divisible by 4, not by 100 -> February has 29 days
if mod(year,4) == 0 & mod(year,100) == ~0;
    if month == 2;
        if 1 <= day <= 29;
            valid = true;
        else
            valid = false;
        end
    elseif month == 1 | 3 | 5 | 7 | 8 | 10 | 12;
        if 1 <= day <= 31;
            valid = true;
        else
            valid = false;
        end
    elseif month == 4 | 6 | 9 | 11;
        if 1 <= day <= 30;
            valid = true;
        else
            valid = false;
        end
    else
        valid = false;
    end
 % leap year: divisible by 400 -> February has 29 days
  
elseif mod(year,400) == 0;
    if month == 2;
        if 1 <= day <= 29;
            valid = true;
        else
            valid = false;
        end
    elseif month == 1 | 3 | 5 | 7 | 8 | 10 | 12;
        if 1 <= day <= 31;
            valid = true;
        else
            valid = false;
        end
    elseif month == 2 | 4 | 6 | 9 | 11;
        if 1 <= day <= 30;
            valid = true;
        else
            valid = false;
        end
    else
        valid = false;
    end
 % normal year -> February has 28 days
    
else
    if month == 2;
        if 1 <= day <= 28;
            valid = true;
        else
            valid = false;
        end
    elseif month == 1 | 3 | 5 | 7 | 8 | 10 | 12;
        if 1 <= day <= 31;
            valid = true;
        else
            valid = false;
        end
    elseif month == 4 | 6 | 9 | 11;
        if 1 <= day <= 30;
            valid = true;
        else
            valid = false;
        end
    else
        valid = false;
    end
end
end

Related Solutions

MATLAB: How to solve this error

You are close, but you forgot that the code below returns an array.

month==[4,6,9,11]

Use parantheses to group your coditions. That should also make it more clear that you don't need that elseif.

Consider create a variable to store the number of days in Feb. Currently your code will reject all non-leap years.

Also, you should replace all & and | by && and || as well.

MATLAB: If else problem for year

All of those if-elseif blocks make the code difficult to read, and difficult to debug as well. I would advise against that approach, and instead tackle each issue one at a time and code only for that issue. That makes the logic of each test much easier to read and to debug. For example, here is an outline of what the code could do using words:

function valid = valid_date(year,month,day)
valid = false; % Set a default return value
% Check for positive integer scalar inputs
if( the year is not a positive integer scalar )
    return;
end
if( the month is not a positive integer scalar )
    return;
end
if( the day is not a positive integer scalar )
    return;
end
% Check for proper month
if( the month is not between 1 and 12 inclusive )
    return;
end
% Construct an array of the number of days in each month
days_in_month = a 12-element array of the number of days in each month;
% Check to see if this is a leap year
is_leap_year = (you put some code here to determine if the year is a leap year)
% If it is a leap year, change February number of days to 29
if( is_leap_year )
    Change the days_in_month value for February to 29
end
% Check to see if the day number is valid
if( the day is greater than the number of days in the month )
    return;
end
% Passed all of our checks, so the date must be valid
valid = true;
return;
end

Once you are satisfied that the words do what you want (you should check this yourself ... maybe I missed something that needs to be checked), then you need to write actual code for all of the worded places. The code you write for this outline will in many places be pieces of the code you have already written in your if-elseif blocks above.

Best Answer

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MATLAB: How to solve this error

MATLAB: If else problem for year

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