How to write a function to determine if a date entered is valid

I am to Write a function called valid_date that takes three positive integer scalar inputs year, month, day. If these three represent a valid date, return a logical true, otherwise false. The name of the output argument is valid. If any of the inputs is not a positive integer scalar, return false as well. Here is the code i have tried but keeps returning true for all dates, I have editted it a lot and now i just need a fresh eye to point out what i am doing wrong:

NB: I am not to use any built in MatLab function.

function valid = valid_date (year, month, date)
if (nargin==3)
    valid=true;
elseif (isinteger(year)) && year>0 && (isscalar(year))
    valid=true;
elseif (isinteger(month))&& month>0 && month <=12 && (isscalar(month))
    valid=true;
elseif (isinteger(date)) && date > 0 && (isscalar(date))
    valid=true;
elseif (month==1||month==3||month==5||month==7||month==8||month==10||month==12)&& date<=31
    valid=true;
elseif date <=30
    valid=true;
elseif (isinteger(year/4)) && month == 2 && (~(isinteger(year/100))||(isinteger(year/400))) && date <= 29
    valid=true;
else
    valid = false;
end

[Image Analyst]

isinteger() and isscalar() are built-in functions.

Also, you can't just say it's valid after checking the year alone or the number of inputs. You have to check the months and days also.

[Elliot Ogbechina]

so do i need to take out all the "valid = true" lines?

[Stephen Cobeldick]

"so do i need to take out all the "valid = true" lines?"

No, you need to revise your logic. For example, the very first thing your function does is check if three inputs were provided:

function valid = valid_date (year, month, date)
if (nargin==3)
    valid=true;
elseif ...
...
end

and if there are three inputs then you set valid=true and exit the function. So I could provide any three inputs and your function would set valid=true ... is that what your assignment required?

[Walter Roberson]

You can arrange the code as a cascade of rejections, each step declaring that valid is false if conditions were not met. Then at the very end when all possible rejections had been processed, anything left over must be valid.

[Elliot Ogbechina]

Okay, I get now. I will find a way to cascade it as rejections and see how it goes. Thank you Walter. Stephen, that's not what I want, I will try and work on it!

[Elliot Ogbechina]

Hello Walter, I tried doing that and everything returns false now.

Here is the code

function valid = valid_date (year, month, date)
if (nargin~=3)
    valid=false;
elseif ~(isinteger(year)) && year>0 && (isscalar(year))
    valid=false;
elseif ~(isinteger(month))&& month>0 && month <=12 && (isscalar(month))
    valid=false;
elseif ~(isinteger(date)) && date > 0 && (isscalar(date))
    valid=false;
elseif ~(month==1||month==3||month==5||month==7||month==8||month==10||month==12)&& date<=31
    valid=false;
elseif ~(date <=30)
    valid=false;
elseif ~(isinteger(year/4)) && month == 2 && (~(isinteger(year/100))||(isinteger(year/400))) && date <= 29
    valid=false;
else
    valid = true;
end

[Walter Roberson]

https://www.mathworks.com/help/matlab/ref/isinteger.html

TF = isinteger(A) returns logical 1 (true) if A is an array of integer type. Otherwise, it returns logical 0 (false).

Not integer value, integer type

[Elliot Ogbechina]

so what can i use in place of isinteger

[Stephen Cobeldick]

"so what can i use in place of isinteger"

Take a look at this answer you were given six hours ago:

https://www.mathworks.com/matlabcentral/answers/498288-how-to-write-a-function-to-determine-if-a-date-entered-is-valid#answer_408221

Does it use isinteger? (hint: no)

What does it use? (hint: mod)

Also read my comment following that answer.

Answer 1

[Jalaj Gambhir]

Hi,

You can try the following function and see if it works for you:

function valid = valid_date(year, month, date)

if(nargin ~= 3)
    valid = false;
elseif (~(mod(year,1)==0) || (year<0) || ~isscalar(year))
    valid = false;
elseif (~(mod(month,1)==0) || (month<=0) || (month>12) || ~isscalar(month))
    valid = false;
elseif (~(mod(date,1)==0) || (date<=0) || ~isscalar(date))
    valid = false;
elseif( (month==1||month==3||month==5||month==7||month==8||month==10||month==12)&& date>31 )
    valid = false;
elseif ((month==4||month==6||month==9||month==11) && date>30)
    valid = false;
elseif(~leapyear(year) && month==2 && date>28)
    valid=false;
elseif(leapyear(year) && month==2 && date>29)
    valid=false;    
else
    valid = true;    
end

[Stephen Cobeldick]

This answer has a few bugs in it, for example, the order of these arguments:

(~(mod(year,1)==0) || (year<0) || ~isscalar(year)

means that if year is non-scalar the code will throw an error (as inputs to the short-circuiting || must be scalar). The solution is to read the || documentation and check isscalar first, then the code will work as specified by the assignment:

~isscalar(year) || ...

The function leapyear is in the Aerospace Toolbox, which is unlikely to be available to most MATLAB users.

Rather than this obfuscation

~(mod(year,1)==0)

prefer the simpler

mod(year,1)~=0

Rather than repeating code:

month==1||month==3||month==5||month==7||month==8||month==10||month==12

just use basic MATLAB vector operations:

any(month==[1:2:7,8:2:12])

[Elliot Ogbechina]

Hello, I have worke on it and i am not supposed to use any date function already in matlab, but the leap year still gives me errors for some inputs.

This is my function

function valid = valid_date(year, month, date)
if(nargin ~= 3)
    valid = false;
elseif ((~isscalar(year)||(mod(year,1)~=0) || year<0))
    valid = false;
elseif ((~isscalar(month))||(mod(month,1)~=0) || (month<=0) || (month>12))
    valid = false;
elseif ((~isscalar(date))||(mod(date,1)~=0) || (date<=0))
    valid = false;
elseif(any(month==[1:2:7,8:2:12])&& date>31)
    valid = false;
elseif (any(month==[4,6,9,11]) && date>30)
    valid = false;
elseif(mod(year,4)~=0 && month==2 && date>28)
    valid=false;
elseif((mod(year,4)==0) && (mod(year,400)==0 && mod(year,100)==0) && month==2 && date>29)
    valid=false;    
else
    valid = true;    
end

it still recognizes 1900 as a leap year

[Stephen Cobeldick]

Nice work. Your code is developing nicely.

Leap years are a bit fiddly. One simple approach would be to calculate the date limit number based on the year (i.e. not have a hard-coded 28 or 29), e.g. replace your two leapyear elseif conditions/statements with something like this:

elseif month==2 && date>(28+(mod(year,400)==0 || (mod(year,100)~=0 && mod(year,4)==0)))

[Elliot Ogbechina]

Thanks a lot. That was really a nice way to work around it.

This is the final code and everything worked.

function valid = valid_date(year, month, date)
if(nargin ~= 3)
    valid = false;
elseif ((~isscalar(year)||(mod(year,1)~=0) || year<0))
    valid = false;
elseif ((~isscalar(month))||(mod(month,1)~=0) || (month<=0) || (month>12))
    valid = false;
elseif ((~isscalar(date))||(mod(date,1)~=0) || (date<=0))
    valid = false;
elseif(any(month==[1:2:7,8:2:12])&& date>31)
    valid = false;
elseif (any(month==[4,6,9,11]) && date>30)
    valid = false;
elseif month==2 && date>(28+(mod(year,400)==0 || (mod(year,100)~=0 && mod(year,4)==0)))
    valid=false;    
else
    valid = true;    
end

Thanks a lot once again.