运行了：means<-vector(length = 10000)
for(i in 1:10000) {
+ means[i]<-mean(sample(LENGTH,size = 1000,replace = TRUE))  
+ }
sd(means)

提示：Error: unexpected '}' in:
"+ means[i]<-mean(sample(LENGTH,size = 1000,replace = TRUE))  
+ }"
请教大家哪里出错了呢？太费解了