Swap function returning a number that is not in my array

Question

I am working on a small bubble sort program in C. I am using a swap function and pointers to accomplish my task, my program runs fine. However, I have an issue. My program returns a 0 (which isn't in the array) and doesn't return a 9. I am very confused.

My array is: int values[] = {7, 3, 9, 4, 6, 1, 2, 8, 5};

And my two functions are:

void sort(){
    int i;
    int j;
    for(i = 0; i < (sizeof(values)/sizeof(values[0])); i++)
    {
        for(j = 0; j < (sizeof(values)/sizeof(values[0])); j++)
        {
            if(values[j] > values[j + 1]){
                swap(&values[j], &values[j + 1]);
            }
        }
    }
}// end sort

void swap(int* i, int* j){
    int x = *i;
    *i = *j;
    *j = x;
}//end swap

And finally, after running my program I get:

Before:
7 3 9 4 6 1 2 8 5
After:
0 1 2 3 4 5 6 7 8

What is the solution?

You need to end the inner loop one element earlier, since you refer to values[j+1] inside it. Your last iteration accesses one element past the end of the array right now. — Dmitri
– Dmitri, Commented Jul 7, 2015 at 0:17

Dmitri · Accepted Answer · 2015-07-07 00:23:42Z

6

Your swap function is fine... the problem is that you access outside the array bounds in the inner for loop. In that loop, you have j ranging from 0 to the last array index, so values[j] will be at most the last element of the array... however, you're working with two elements at a time, values[j] and values[j+1]... and on the last iteration, values[j+1] is out of bounds.

The solution is just to stop your inner loop one iteration earlier, ie.:

    for(j = 0; j < (sizeof(values)/sizeof(values[0]) - 1); j++){

answered Jul 7, 2015 at 0:23

Dmitri

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1 Comment

Andy C Over a year ago

Thank you, for some reason I tried for(j = 0; j < (sizeof(values)/sizeof(values[0]) - sizeof(values[0]); j++){ I'm not very familiar with C quite yet, so getting the hang of it all. thank you so much

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