How to use the 'if' statement in matlab?

I have a cell array of size 5x5 as below

 B= 00 10 11 10 11 
    01 01 01 01 11 
    10 00 01 00 01 
    10 10 01 01 11 
    10 10 10 00 10 

And two column vectors

 S1= 21 
     23
     28 
     25 
     43 

 S2= 96 
     85 
     78 
     65 
     76 

I want to create a new cell array of the same size as B say 5x5 such that it satisfies the following condition

  Final={S1 if B{i}=11
         S1 if B{i}=10
         S2 if B{i}=01
         S2 if B{i}=00

So the resulting output would be something like this

  Z = s2 s1 s1 s1 s1   
      s2 s2 s2 s2 s1
      s1 s2 s2 s2 s2
      s1 s1 s2 s2 s1
      s1 s1 s1 s2 s1
ie Z= 96 21 21 21 21 
      85 85 85 85 23 
      28 78 78 78 78
      25 25 65 65 25
      43 43 43 76 43

I tried using the if condition but i get error saying 'Error: The expression to the left of the equals sign is not a valid target for an assignment.'

 for i=1:1:128
   for j=1:1:16
      if fs{i,j}=00
         Z{i,j}=S1{i,j}
      elseif fs{i,j}= 01
         Z{i,j}=S2{i,j}
      elseif fs{i,j}= 10
         Z{i,j}=S1{i,j}
      elseif fs{i,j}= 11
         Z{i,j}=S2{i,j}
        end
     end

I think I'm making a mistake in the if statement as well as the expressions I'm using. Where am i going wrong? Please help thanks in advance.