R If then do - how to create variabes based on the condition

As a dedicated SAS user I struggle with understanding if-then logic in R.

Say, I have a following dataframe

test<-data.frame("year" = c(2018, 2019),
             "var1"=c(1,2),
             "var2"=c(3,4),
             "var3"=c(5,6),
             "var4"=c(7,8),
             "var5"=c(9,10),
             "var6"=c(11,12))

Now, I want to create two additional variables in the following way:

if year is 2018 then extra_var1=var1+var2, extra_var2=var2+var3 if year is 2019 then extra_var1=var4+var5, extra_var2=var5+var6

In SAS I would do:

data test;
set test;
if year=2018 then do;
extra_var1=var1+var2;
extra_var2=var2+var3;
end;
if year=2019 then do;
extra_var1=var4+var5;
extra_var2=var5+var6;
end;
run;

How to do it in R? Is there any other way then nested ifelse?