want to make vectors of same length

Hello, need help in the following problem. BC is 1x99 and a(i), b(i) and c(i) are 1x30. and i want to plot BC vs a(i), but i am getting following error: In an assignment A(:) = B, the number of elements in A and B must be the same. any help much appreciated

data = load(FF); mass = data(:,1); %extracting all rows of column 1 deq = data(:,16); %extracting all rows of column 16

BC = (15:10:995);

for i = 1:length(BC)-1; index = deq>=BC(i)-5 & deq<BC(i)+5; masstemp = mass(index); a(i) = min(masstemp); b(i) = median(masstemp); c(i) = max(masstemp); end