nested if else statements

I have a vector of 2,1,0 I want to change to 0,1,2 respectively (the  
data
is allele dosages)

I have tried multiple nested if/else statements and looked at the ? 
if help
and cannot work out what is wrong, other people have posted code  
which is
identical and they state works.

Any help would be greatly appreciated.

A[1:20]

[1] 1 1 0 0 1 0 1 0 1 0 0 0 1 1 0 1 1 1 0 0

B <- rep(NA,length(A))

for (i in 1:length(A)){ if(A[i]==2){B[i] <- 0} else

+                         if(A[i]==0){B[i] <- 2} else
+                         if(A[i]==1){B[i] <- 1}}

Error in if (A[i] == 2) { : missing value where TRUE/FALSE needed