function?how_many_days?=?days（year1month1day1year2month2day2）
%calculate?days?between?2?dates.
flag?=?is_legal（year1month1day1year2month2day2）;?%cheack?input?parameter?is?legal?or?not.
if（flag?==?1）
????if（year1?????????[year1year2]?=?exchange（year1year2）;
????????[month1month2]?=?exchange（month1month2）;
????????[day1day2]?=?exchange（day1day2）;
????end
????if（year1?>?year2）
????????sum1?=?sum_part1（year1month1day1）;
????????sum2?=?sum_part2（year1year2）;
????????sum3?=?sum_part3（year2month2day2）;
????????how_many_days?=?sum1+sum2+sum3;
????else?????????????????%??the?condition?year1?==?year2.
???????how_many_days??=?sum_same_year（year1month1day1month2day2）;
????end
else
????disp（‘illegal?inputplease?check?your?parameters.‘）
end
end

function??flag?=?is_legal（year1month1day1year2month2day2）
days_every_month1?=get_dem（year1）;
days_every_month2?=get_dem（year2）;
flag1?=?（year1>=0?&&?year2>=0?&&?month1>0?&&?month2>0?&&?day1>0?&&?day2>0）;
flag2?=?（month1<13?&&?month2<13）;
if（flag2?&&?flag1）
????flag3?=?（days_every_month1（1month1）>=day1?&&?days_every_month2（1month2）>=day2）;
else
????flag3?=?0;
end
flag?=?flag1?&&?flag2?&&?flag3;?
end

function?result?=?is_leap_year（year）
if?（（mod（year4）==0）&&（mod（year