Iteration

# for, while, repeat

# examples

> x <- matrix(0, nrow=3, ncol=4)
> for(i in 1:3){ for(j in 1:4){ x[i,j]<-i+j } }

> while(x*2<10000){ x<-x*2; i<-i+1 }

> repeat{ i<-i+1; x<-x*2; if(x*2>10000) break }

> y <- NULL
> for(i in 1:3) { y<-y+i; cat('i is',i, '\n') }