%function to detrmine the number of A's , C's, G's and U's in a RNA string D
function [As,Cs,Gs,Us] = frna(D)
As=0;
Cs=0;
Gs=0;
Us=0;
for i = 1:length(D)
    if (D(i)== 'A')
        As = As+1;
    elseif (D(i)== 'C')
        Cs = Cs+1;
    elseif (D(i)== 'G')
        Gs = Gs+1;
    elseif  (D(i)== 'U')
        Us = Us+1;
    end;
end;