There are two errors in your code
1) Bracket at wrong position (causes your problem to stay at 128 all the time)
mult(1,k) = mult(1,k)*2^(length(base2)-k)
2) Obsolete Increase in loop variable. If you have a for loop, Matlab increases the variable by itself (check the docu). So the following has no effect, since Matlab simply overwrites your changes.