[R] writing several command line in R console

[Vincent Stoliaroff]

Hi R lovers

I would like to know how to step to the next line in the R console editor 
without breaking the continuity of my code
more clearly : if for example I write a function, so far i have to write the 
all code inside on the same line wich may become obscure as the function is 
more and more complex.
I would like to do like in the example of the manuels:

>twosam <- function(y1, y2) {
    n1  <- length(y1); n2  <- length(y2)
    yb1 <- mean(y1);   yb2 <- mean(y2)    s1  <- var(y1);    s2  <- var(y2)
    s <- ((n1-1)*s1 + (n2-1)*s2)/(n1+n2-2)
    tst <- (yb1 - yb2)/sqrt(s2*(1/n1 + 1/n2))    tst  }


all I can do is something like that:

>twosam <- function(y1, y2) {    n1  <- length(y1); n2  <- length(y2)

+    yb1 <- mean(y1);   yb2 <- mean(y2)    s1  <- var(y1);    s2  <- var(y2)
+    s <- ((n1-1)*s1 + (n2-1)*s2)/(n1+n2-2)
+   tst <- (yb1 - yb2)/sqrt(s2*(1/n1 + 1/n2))    tst  }

with the sign "+" in front of each line
What does this sign mean? and how could I solve my problems
Thanks