x<-1:20
Num<-function(x){
stopifnot(is.numeric(x))
k<-sum(x%%2==0)
return(k)
}
Num(x)
x<-1:20
Num<-function(x){
k=0
stopifnot(is.numeric(x))
for (i in 1:length(x)) {
if(i%%2==0){
k=k+1
}
}
return(k)
}
Num(x)