Getting two outputs instead of one in Matlab

Question

The question here was to find if the date provided is a valid one or not without using native Matlab date functions. I was hoping if someone can point out my mistake here. I'm also getting the "Output argument valid (and maybe others) not assigned during call to valid_date " error in Matlab learning tool when I submit it.

function valid = valid_date(year,month,day)

if nargin~=3
    valid = false;
elseif ~isscalar(year)||year<1||year~=fix(year)
    valid = false;
    return
elseif ~isscalar(month)||month<1||month~=fix(month)
    valid = false;
    return
elseif ~isscalar(day)||day<1||day~=fix(day)
    valid = false;
    return
elseif month>12 || day > 31
    valid = false;
end

if ((mod(year,4)==0 && mod(year,100)~=0) || mod(year,400)==0)
    leapdata=1;
else
    leapdata=0;
end

%the below if statements are used to define the months. Some months have 
%31 days and others have 30 days, while February has only 28 days and 29 on
%leap years. this is checked in the below code.
% I feel the below code is where the error is.

if ismember (month, [1 3 5 7 8 10 12])
    ismember (day, (1:31))
    return
elseif ismember( month, [4 6 9 11])
    ismember (day, (1:30))
    return
end


if month == 2
    if leapdata==1
        ismember (day, (1:29))
        return
    elseif leapdata==0
        ismember (day, (1:28))
        return
    else
        valid = false;
    end 
end

Answer 1

When returning at the end of a Matlab function, the value of the variable valid is sent as an output. In the lines below the four comments, you need to assign the variable to true or false inside of the if statements. For example:

if ismember(month, [1 3 5 7 8 10 12])
    valid = ismember(day, (1:31))
    return
elseif ismember(month, [4 6 9 11])
    valid = ismember(day, (1:30))
    return
end


if month == 2
    if leapdata == 1
        valid = ismember(day, (1:29))
        return
    elseif leapdata == 0
        valid = ismember(day, (1:28))
        return
    else
        valid = false;
    end 
end