Im trying to get a column vector with a list of composite numbers within a random range using the randi function but I keep getting an error.

My project is creating two BINGO cards that compete with eachother to see who wins first. The columns need to consist of composite numbers within a 20 number range (for B column its composite numbers that are in 1-99 but I must create a column vector to find all composite numbers within a 20 number range within the 1-99 range).

Here is code for B column vector for card 1:

%getting numbers in random range for both card1 B column
randB1 = randi([1 99]);
i = 0;
while i < 1
    if (randB1 - 20) < 0
        randB1 = randi(length(B));
    else
        rangeB1 = [randB1-20 randB1]; %checking to make sure first range number isnt <0
        i= i +1;
    end
end

%organizing range to put in Bcol1
if isprime(rangeB1(1))
    rangB1=find(c==rangeB1(1)+1);
else
    rangB1=find(c==rangeB1(1));
end
if isprime(rangeB1(2))
    rangB2=find(c==rangeB1(2)-1);
else
    rangB2=find(c==rangeB1(2));
end
Bcol1=c(rangB1:rangB2)';

randB2 = randi([1 99]);

This is the error I'm getting:

Error using randi

First input must be a positive scalar integer value IMAX, or two integer values [IMIN IMAX] with IMIN less than or equal to IMAX.

Error in Project (line 289)

r2 = randi([1,length(Bcol2)]);

[Michael Price]

The last error message is further in the code but I believe the problem is coming from the if statement because the Bcol2 is coming up as [] in the code when there should be numbers in it. Sometimes it works sometimes it doesn't I just want it to be consistent every time, and ignore the Bcol2, it should Bcol1 but its the same code for finding Bcol1 I'm just getting errors for each col variable and solving one should help solve the other.

[the cyclist]

Your code gives me an error (not the one you are concerned about) because it cannot find the variable c. It would also be helpful (to yourself as well as us) to comment each line of code in more detail, explaining exactly what you intend it to do. I'm finding it difficult to follow the logic.

[Walter Roberson]

You are choosing randomly. The values are not always going to be in increasing order but you use the values in a colon operation that is going to return empty if the second is less than the first.

[Michael Price]

how would I fix that? That's probably what's causing the problem for everything.

[Michael Price]

Would this code fix the problem?

if rangB1 > rangB2

Bcol1=c(rangB2:rangB1)';

else

Bcol1=c(rangB1:rangB2)';

end

[Walter Roberson]

Consider using sort()

[Michael Price]

So like this?

Bcol1=c(sort(rangB1:rangB2))';

[Walter Roberson]

temp = sort([rangB1, rangB2])
temp(1):temp(2)

[Michael Price]

Would I then put temp inside of Bcol1 = c( )';?

[Walter Roberson]

temp = sort([rangB1, rangB2])
Bcol1 = c(temp(1):temp(2)).';

Answer 1

[Walter Roberson]

for K = 1:20:99
    range = K:K+19;
    composites = setdiff(range(~isprime(range)),1);   %1 is never prime
    composites(randperm(length(composites),5))
end

ans = 1×5

15 10 9 18 8

ans = 1×5

25 30 39 32 34

ans = 1×5

42 50 52 49 58

ans = 1×5

69 65 63 62 66

ans = 1×5

95 88 91 90 82