Can anyone point out the mistake in this program? It's regarding writing a function to check if the entered date is valid or not.

Here is the code that I have written, but it gives wrong answers for date such as 31st April 2018 (2018,4,31). Ideally the program should give me logical 0, however, it gives me logic 1.

function [valid]=valid_date(year, month, day)
if isscalar(year) && year>0 && year~=0 && isscalar(month) && month>0 && month~=0 && isscalar(day) && day>0 && ar
    if mod(year,4) == 0 && mod(year, 100)~= 0 || mod(year,400)==0 && month==2 && days<=29 
    %for february
         valid=true;
    else
        valid=false;
    end
    %for rest of the months
    if month==4 || month==6 || month==9 || month==11 && day<=30
             valid=true;
    elseif month==1 || month==3 || month==5 || month==7 || month==8 || month==10 || month== 12 && day<=31
             valid=true;
    else
        valid=false;
    end
    
    %not a leap year
    if month==2 && day>28
        valid=false;
    end
    %rest of the months
    if month==4 || month==6 || month==9 || month==11 && day<=30
             valid=true;
    elseif month==1 || month==3 || month==5 || month==7 || month==8 || month==10 || month== 12 && day<=31
             valid=true;
    else
             valid=false;
    end
    
else
    valid=false;
end 

[Jan]

See this duplicate question also:

https://www.mathworks.com/matlabcentral/answers/453107-how-can-i-solve-this-can-anyone-provide-me-with-code-whats-wrong-with-my-code

Answer 1

[praveen]

it has to be

if (month==4 || month==6 || month==9 || month==11) && day<=30
             valid=true;
    elseif (month==1 || month==3 || month==5 || month==7 || month==8 || month==10 || month== 12) && day<=31
             valid=true;
    else
        valid=false;
    end

Use Parentheses generously. It is a good idea to use parentheses to explicitly specify the intended precedence of statements containing combinations of & and |

[Jan]

There are much more errors in the code. E.g. the first test fails, because the if condition ends with the meaningless "&& ar".