function day_step(old_day,step)
local y,m,d
if("0" ~= string.sub(old_day,6,6)) then
m=string.sub(old_day,6,7)
else
m=string.sub(old_day,7,7)
end
if("0" ~= string.sub(old_day,9,9)) then
d=string.sub(old_day,9,10)
else
d=string.sub(old_day,10,10)
end
y=string.sub(old_day,0,4)
local old_time=os.time{year=y,month=m,day=d}
local new_time=old_time+86400*step
local new_day=os.date("*t",new_time)
local res=""
if(tonumber(new_day.day)<10 and tonumber(new_day.month)<10)then
res=new_day.year.."-".."0"..new_day.month.."-".."0"..new_day.day
elseif tonumber(new_day.month)<10 then
res=new_day.year.."-".."0"..new_day.month.."-"..new_day.day
elseif tonumber(new_day.day)<10 then
res=new_day.year.."-"..new_day.month.."-".."0"..new_day.day
else
res=new_day.year.."-"..new_day.month.."-"..new_day.day
end
return res
end