If else problem for year

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. Note that every year that is exactly divisible by 4 is a leap year, except for years that are exactly divisible by 100. However, years that are exactly divisible by 400 are also leap years. For example, the year 1900 was not leap year, but the year 2000 was.

valid = valid_date(2018,4,1)
valid = valid_date(2018,4,31)

[Rik]

You can find guidelines for posting homework on this forum here.

[RAHUL ANTIL]

I know this is my homework but I've tried my best. I'm getting problem in leap year part.

[Rik]

Have you seen my answer below? Also, what is your problem with determining if a year is a leap year? If you don't know about it yet: the mod function could be very helpful.

[RAHUL ANTIL]

Here is my function-

I need help that if non-scalar value is used then ouput is false.

function valid = valid_date(year,month,day)
if (isinteger(year/4) || ~isinteger(year/4)) && ((month == 1) || (month == 3) || (month == 5) || (month == 7) || (month == 8) || (month == 10) || (month == 12)) && (day>0 && day<=31)
    valid = true;
elseif (isinteger(year/4) || ~isinteger(year/4)) && ((month == 4) || (month == 6) || (month == 9) || (month == 11)) && (day>0 && day<=30)
    valid = true;
elseif mod(year, 400) == 0 && month == 2 && (day>0 && day<=29)
    valid = true;
elseif mod(year, 4) == 0 && mod(year, 100) ~= 0 && month == 2 && (day>0 && day<=29)
    valid = true;
elseif ~(mod(year, 400) == 0) && month == 2 && (day>0 && day<=28)
    valid = true;
elseif ~(mod(year, 4) == 0 && mod(year, 100) ~= 0) && month == 2 && (day>0 && day<=28)
    valid = true;
else
    valid = false;
end

[Matthew Myers]

Hello everyone, I wanted to post my attempt at this and try to understand my mistakes in writing my code.

I notice that during the function, the month does not trigger the "limit" variable that I have set and I cannot understand why. I would appreciate any help with this.

I tried to take your advice Rik in takling each issue one at a time, but I didn't go about it in the right way

function[out] =  valid_date(year,month,day)
    out = false
    if nargin<3
        return
    elseif ~isscalar(year) || year<1 || year ~= fix(year)
        return
    elseif ~isscalar(month) || month<1 || month>12 || month ~= fix(month)
        return
    end
    
    persistent limit;
    if isempty(limit), limit = 0;end
    if month == (1:2:11)
        limit = 31;
    elseif month == (4:2:12)
        limit = 30;
    elseif month == 2
        limit = 28;
    end
    
    %leap year part. Month must be february
    if year == (0:4:3000) && month == 2
        limit = 29;
    elseif year == (0:100:3000) && month == 2
        limit = 28;
    else year == (0:400:3000) && month == 2
        limit = 29;
    end
    
    if ~isscalar(day) || day<1 || day>limit|| day ~= fix(day)
        return;
    end
    
    if isscalar(day) && day>=1 && day<=limit
        out = true;
    end
end

[Rik]

I don't understand your indentation and why you are using a persistent variable. I would also suggest to always make sure that conditionals are scalar. I would also suggest making sure your code can handle dates beyond the year 3000.

Did you use the debugger to step through your code line by line?

Answer 1

[James Tursa]

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.

[RAHUL ANTIL]

Thanks James Tursa

[Elliot Ogbechina]

I really dont know where i am getting this wrong...i have tried a lot that right now i just need a fresh pair of eyes. It never seems to return false. Here is my code;

function valid = valid_date (year, month, date)
if (nargin==3)
    valid=true;
elseif (isinteger(year)) && year>0 && (isscalar(year))&&(isinteger(year/4)) && month == 2 && (~(isinteger(year/100))||(isinteger(year/400)))
    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 is_leap_year == true && date <= 29
    valid=true;
else
    valid = false;
end

[Steven Lord]

If the first if condition is true, your elseif and else statements never get executed. You don't "fall through" as I suspect you expected. You could use a series of if statements with return statements inside.

if nargin < 3
  valid = false;
  return
end

Instead of calling return each time you could check if the date has passed all previous checks. If it failed one of the previous checks, later checks can't make it valid again.

valid = true;
if valid && nargin < 3
  valid = false;
end
if valid && nextDisqualifyingCondition
  valid = false;
end

Yes, the check of valid in the first block isn't technically necessary since the previous line set it to true but it shows the technique.

[Ashwin Raju]

Hello, I just need help with my code I am very bad at programming and am learning. Using your idea I wrote this code. I humbly ask your help in figuring out what is wrong with this as it is only showing valid results for non-scalar inputs and random non-leap years.

function valid = valid_date(y, m, d)
valid = false;
if ~isinteger(y) || y < 1
    return;
end
if ~isinteger(m) || m < 1
    return;
end
if ~isintiger(d) || d < 1
    return;
end
if m < 1 || m > 12
    return;
end
b = [31 28 31 30 31 30 31 31 30 31 30 31];
p = rem(y,4);
q = rem(y,100);
r = rem (y,400);
if ((p == 0 && q ~=0) || r == 0)
    b = [31 29 31 30 31 30 31 31 30 31 30 31];
end
if d > b
    return;
end
valid = true;
end

[Rik]

You aren't selecting the number of days in a month. d>b is comparing a scalar to a vector, which is probably not doing what you think it is.

I still think mlint should issue a warning if you try to use a non-scalar as the condition of an if or a while.

[Ashwin Raju]

Thank you for the help but still not able to get the output. I even tried 'd > b(m)' instead of 'd > b' among a lot of other things.

[MOHD FARHAN]

This is showing error please help

[Rik]

What did you try? The code posted in this answer is not the finished code you can hand in. It is meant as a guide to help you get a solution on your own.

[Adonis Thirafi Hugo Mafaza]

Hello @Rik, I still don't get why we need to assign valid = false right after and below after we define the function valid_date(...). Could you please explain it?

[Rik]

You don't need to, it is just an easy method. If you do assign false as a kind of default value, you can simply use return to exit the function and say the date is invalid.

[Rik]

You are actually explicitly writing on the public internet that you want to cheat? I admire your courage.

You are correct: it would be much faster to copy code by someone else. However, you would not learn. Next time you will need someone else to make your homework again. If you are in a hurry, that probably means you delayed doing your homework. Why should others come to your rescue?

Answer 2

[Muthu Dhanush Santh Nagarajan]

I have tried this program and i got all the answers correct. Please check

function valid=valid_date(y,m,d)
    valid = false;
    if(((isscalar(y) && y>=1 && y==fix(y))&& (isscalar(m) && m>=1 && m==fix(m) && m<=12)...
            && (isscalar(d) && d>=1 && d==fix(d) && d<=31))==1)
        c1= (ismember(m,[4,6,9,11]) && ismember(d,[1:30]));
        c2=(ismember(m,[1,3,5,7,8,10,12]) && ismember(d,[1:31]));
        if ((c1==1 || c2==1)==1)
            valid = true;
        else
            if ((mod(y,4)==0&&mod(y,100)~=0 || mod(y,400)==0&&mod(y,100)==0)==1)
                if (ismember(d,[1:29])==1)
                    valid = true;
                end
                return;
            else
                if (ismember(d,[1:28])==1)
                    valid = true;
                end
                return;
            end
        end
    end
end

[Rik]

This function is missing documentation.

And what are the exact requirements of your assignment? You should try to create a test-suite that contains syntaxes that should work and return truie or false, and sytaxes that should return an error.

Also, do you have a question? Because you posted this in the answer section.

[Mohammad Aiyoob Rahmani]

this code is right

it is working properly

[abdul kabeer]

This is good

Answer 3

[Salman P H]

function valid = valid_date(x,y,z)
t = (isscalar(x) && isscalar(y) && isscalar(z));
if t==false
    valid = false;
    return;
end
if (x<=0 || y<=0 || z<=0)
    valid = false;
    return;
end
if any(rem([x, y, z], 1))
    valid = false;
    return;
end
if (((rem(x,4)==0) && (rem(x,100)~=0)) || (rem(x,400)==0))
    a=1;
else
    a=0;
end
if (x>0) && a==1
    if (y==1 || y==3 || y==5 || y==7 || y==8 || y==10 || y==12) && (z>0 && z<=31)
        valid = true;
    elseif (y==4 || y==6 || y==9 || y==11) && (z>0 && z<=30)
        valid = true;
    elseif (y==2 && (z>0 && z<=29))
        valid = true;
    else
        valid = false;
    end
elseif x>0 && a==0
    if (y==1 || y==3 || y==5 || y==7 || y==8 || y==10 || y==12) && (z>0 && z<=31)
        valid = true;
    elseif (y==4 || y==6 || y==9 || y==11) && (z>0 && z<=30)
        valid = true;
    elseif (y==2 && (z>0 && z<=28))
        valid = true;
    else
        valid = false;
    end
end

[arjun gupta]

Perfect :))

[khaula]

after trying all other codes, i found this one correct. thanks

Answer 4

[Rik]

You can do this two ways:

Option 1 is to do the actual work. Is the input correct? Does the month entered actually have at least as many days as the day input (taking leap years into account)?

Or option 2: cheat by using the builtin functions to convert your input to a datetime scalar, and extract the year,month,day numbers from that. If those match the input, your date is valid. You should still put in a check if the inputs are positive scalars.

[Divya Nangaru Sudhakar]

function valid = valid_date(year,month,day)
if (isinteger(year/4) || ~isinteger(year/4)) && ((month == 1) || (month == 3) || (month == 5) || (month == 7) || (month == 8) || (month == 10) || (month == 12)) && (day>0 && day<=31)
    valid = true;
elseif (isinteger(year/4) || ~isinteger(year/4)) && ((month == 4) || (month == 6) || (month == 9) || (month == 11)) && (day>0 && day<=30)
    valid = true;
elseif mod(year, 400) == 0 && month == 2 && (day>0 && day<=29)
    valid = true;
elseif mod(year, 4) == 0 && mod(year, 100) ~= 0 && month == 2 && (day>0 && day<=29)
    valid = true;
elseif ~(mod(year, 400) == 0) && month == 2 && (day>0 && day<=28)
    valid = true;
elseif ~(mod(year, 4) == 0 && mod(year, 100) ~= 0) && month == 2 && (day>0 && day<=28)
    valid = true;
else
    valid = false;
end

i used the same code but its showing that

"Non-scalar

Variable valid has an incorrect value.

Return false if an input is not scalar..."

Can anyone please help me with the modification of the code.

Thank you

[Rik]

Why are you using neither my suggestion, nor James's?

Also, this is input checking, which you should do before any other processing. Read about the numel function

[Divya Nangaru Sudhakar]

I tried executing that function explained by James's, I dint get the output. Can you please help me with this function.

Thank you

[Rik]

James didn't provide a full function, because it is a homework exercise. If you want me to make your homework, first make sure I'll get the points from your teacher. (You can find guidelines for posting homework on this forum here.)

Did you read the documentation for numel? And how did you try to implement either my solution or the solution by James?