Note: Containing loop

[Tduck]

This code compiles and runs, outputs what I want, but still produces an error. From what I understand this is undefined behavior, but to me this all seems pretty novel, all pretty understandable. What doesn't my compiler understand about it?

errors:
14:9, note: contains loop.
warning: iteration 9u invokes undefined behavior

I also did figure out how to make the errors go away, in that I changed the maximum i iteration to be 8, or less than 9, but why is it considered a bad practice to rerun the loop in case you didn't end up sorting it properly, say I had user input?

#include <iostream>

using namespace std;

int main()
{
    //to bubble sort, run through an array, record a value, if it's lower than the next, keep it, if higher than the next, swap it.  
    //redo this length times.  
    int intArray[10] = {10,9,8,7,6,5,4,3,2,1};
    int temp;
    for(int j = 0; j < 10; j++)
    {
        for(int i = 0; i < 10; i++)
        {
            if(intArray[i] > intArray[i+1]) 
            { 
                temp = intArray[i];
                intArray[i] = intArray[i+1];
                intArray[i+1] = temp;
            } 
        }
    }
    for(int i = 0; i < 10; i++)
    {
        cout << "Int array " << i << ":  " << intArray[i] << endl;
    }
}

[jlb]

Your accessing your array out of bounds on lines 15, 18, and 19 on the last iteration of the loop because of the addition.

[lastchance]

You have declared intArray[] to have size 10. Indices count from 0 (in c++) so its elements are
intArray[0]
intArray[1]
.
.
intArray[9]

In your inner loop i <10, so the largest value is i=9.
On line 15 you then compare intArray[9] with ... intArray[10].
But intArray[10] doesn't exist.

So, your compiler is actually being quite kind to you, don't you think?

[Tduck]

Would my code run and sort fine if I set the iterations down by 1? That's what I have it at now.

[lastchance]

Yes

Actually, you can do better. Each pass puts another "sorted" one at the end, so:
(1) Once you've put the largest 9 in place, the final one is automatically in place. So you need 9 (or, in general, size-1) passes in j. Thus j=0 and j<9 would be Ok here.
(2) Each pass doesn't have to be as long, since each pass puts another one in a sorted position at the end. Hence, the i loop doesn't need to be as long; the loop condition could be i<9-j.

And it would be better if you didn't use the "magic number" 10.
Set
const int size = 10;
at the start and then (after making the changes above) replace every 10 by size, and every 9 by size-1.