function f=isleapyear(year)
sign=0;
if rem(year,4)==0
    sign=sign+1;
end
if rem(year,100)==0
    sign=sign-1;
end
if rem(year,400)==0
    sign=sign+1;
end 
if sign==1
    fprintf('%d  is a leap year.\n',year)
end

运行时：??? Input argument 'year' is undefined.

Error in ==> D:\matlab\matlab\work\isleapyear.m
On line 5  ==> if rem(year,4)==0
why??????????????????????????????