A=0:7;
Sbox=[0,1,3,6,7,4,5,2];
N = length(A);
X=de2bi(A,3,'left-msb');
U=[];
% res=[];
% w1=[];
for i=1:N
U(i,:)=xor(X(i,:),X(2,:));
% res=bi2de(U,'left-msb')'
end
res=bi2de(U,'left-msb')'; % calculate res once, for all U, after the loop
s_out=[];
for i=1:N
% s_out = sbox(res(i));% error in this line
s_out(i) = Sbox(res(i)+1); % - the variable is Sbox, not sbox (MATLAB is case-sensitive)
% - add 1 to res(i) to use as index into Sbox (res starts at 0, index start at 1)
% - assign the result to s_out(i), i.e., a single element of s_out
end
s_out
