days_monthday<-function(date)
{
m<-format(date,format="%m")
days31<-c("01","03","05","07","08","10","12")
days30<-c("04","06","09","11")
days29<-c("02")

if(m %in% days31) return(31)
if(m %in% days30) return(30)
if(m %in% days29) return(29)
}
days_monthday1<-function(date)
{
m<-format(date,format="%m")
while(format(date,format="%m")==m)
{
date<-date+1
}
return(as.integer(format(date-1,format="%d")))
}
date<-as.Date("2017-4-11","%Y-%m-%d")
date
days<-days_monthday(date);days
day<-days_monthday1(date);day