Lotto code,the previous number cannot appear again,how do i improve it?

i want to write a lotto code,and there are six numbers in it,the range of first six numbers is 1 to 38,the range of last number is 1 to 8.Here is my code

x = rand(1,10);
[a b]=sort(x);
previous_number=b(1:6)
last=randi([1,8],1,1) %produce the last number

for k =1:6    
    while  last== b(k)%while that last number is the same as the value of one of the previous number
    last=randi([1,8],1,1)%then produce the last number again,until the different value produce
    end
end
ltto=[previous_number last]

but i found that the last number will still generate the same number as the first six numbers,for example,

"1" 2 33 55 66 10 "1"

1 "2" 33 55 66 10 "2"

Why?i have already said

while  last== b(k)
    last=randi([1,8],1,1)
    end   

how do i improve it? i don't want to use the "randperm"

Answer 1

[Torsten]

x = rand(1,10);
[a b] = sort(x);
previous_number = b(1:6)
set_for_last_number = setdiff(1:8,previous_number);
pos = randi(length(set_for_last_number));
last = set_for_last_number(pos)

[yang-En Hsiao]

your answer is great,but if i can't use the setdiff,maybe because the version is too old,how do i write this code by using maybe like while ,for or if loop?

[madhan ravi]

Wow yang why is it so hard to admit that it’s your homework?

[yang-En Hsiao]

because i think i can't rely on the matlab functions too much,although they are very convenient.I believe it can be written even we don't use the function like " setdiff " or " randperm " .Like C or other programs,there is no so convenient function like " setdiff " and " randperm "