If then else in R

I am an old dog struggling with R as a new trick

I want to replicate the follow SAS code in R (using a dataframe with multiple columns):-

if sum5 > 0 then gbind = 1;
else if  sum4 > 0 then gbind = 2;
else if block19 in ('B') then gbind = 3; (many other elements)
else gbind = 0;

Please Help