Exceeding matrix dimensions for a sorting algorithm, how do I run through an entire array with just a single for loop?

Hello, so I have been trying to work on a very basic sorting algorithm that just goes thru an array of 'N' numbers and sorts them in ascending order. We can't use any built in sort functions and we get a bonus point for using a single for loop. I decided to go with a Bubble sort since I know how that works, but I don't know how to make it so that the for loop can go thru an array of any size. Here's what I have so far:

    a = [1 9 2 8 3 7 4 6 5]; %My array
    b = a; %temp variable  

    [a1, a2] = size(a); %gets the length of array

    for i = 1:a2 %ensures the loop goes all the way thru the array

        if a(i+1) < a(i) %checks if the follow value is greater than the lead
            b(i) = a(i); %if so sets the lead value to the temp value
            a(i) = a(i+1); %sets first value to follow value
            a(i+1) = b(i); %sets follow value to first value 
        end
    end

    a

I understand what's wrong with this, that as the for loop approaches the end of the array, the a(i+1) exceeds the limit of the array's size. But I'm just really stuck on how I am suppose to be able to do this for any sized array. If anyone could provide any help I would greatly appreciate it. Thanks!

[Cedric]

 a2 = 10 ;
 1 : a2
 1 : a2-1

outputs:

 ans =
     1     2     3     4     5     6     7     8     9    10

 ans =
     1     2     3     4     5     6     7     8     9

but if I remember well, it will be tricky to implement bubble sort using a single explicit loop!