function [prime] = isPrime( N )
%ISPRIME written as a function rather than just loose code

% we will assume to start off with that the number IS prime, then check to see if it isn't

% Prime=1 is horrible.. true/false is the way forward!
prime=true;

% This is a loop. I think the easiest way of thinking about this is that you are saying for all i in {2...n/2} (using maths notation)
% The loop will perform all the code between "for" and "end" incrementing the value of i each time.
for i=2:N/2

   % This checks to see if i divides N (the number we are testing for primality. If it does, we set prime to 0. Otherwise we skip to !(A)!
   % This is a conditional statement. The syntax "if" `condition` .... end will perform all the code in .... iff the condition is true
   if mod(N,i)==0

      % N is not a prime number so set prime=false
      prime=false;

      % break jumps out of the for all loop. You can delete this and the algorithm will work.. it is just an optimisation.
      break

   end

% !(A)! If i does NOT divide N, the computer will jump here, the end will make it go to the next value of i in {2, .. ,N/2}
end

% if prime=true N is a prime number
if prime==true
   disp('Prime Number!')

% if prime=false N is NOT a prime number
else
   disp('Not a Prime Number!')
end

end