Thread: Program to print the numbers in ascending order

The idea is that if two elements are out of order, you swap them. The loops are there to mainly make sure that enough swaps happen.

The worst case for bubble sort, an array that is in reverse order from sorted, is actually instructive, since it will mimic the sort written down very closely.

Start with the first two, swap if they are bold. Proceed to the next two numbers. If the numbers are fine, proceed without a swap.
5 4 3 2 1
now the array is: 4 5 3 2 1
4 5 3 2 1
4 3 5 2 1
4 5 3 2 1
4 5 2 3 1
4 5 2 3 1
4 5 2 1 3
The first two are technically in order, go to next swap.
4 5 2 1 3
4 5 1 2 3
Again, first two are in order.
4 5 1 2 3
4 1 5 2 3
4 1 5 2 3
4 1 2 5 3
4 1 2 5 3
4 1 2 3 5
4 1 2 3 5
1 4 2 3 5
1 4 2 3 5
1 2 4 3 5
Again, we have a lot of elements in order.
1 2 4 3 5
1 2 3 4 5

It's called bubble sort because the smaller items gradually move, bubbling up, to the front of the array.

And that is basically bubble sort. Wikipedia has a nice animation of a bubble sort happening.

Originally Posted by abhi143

There are two for loop. What does they do ?

The inner loop loops over the entire array (other than the last element, because on each iteration, the current element is compared with the next element, so you cannot loop until the last element because that element has no next element). The effect of this is to move the elements a little closer to the sorted order, e.g., if the largest value was stored in the first element, it would be "pushed" all the way back to be stored in the last element. Hence, one idea is to run the inner loop many times until the array is sorted, and one way (though not the most efficient way) of doing that is to always run the entire inner loop almost as many times as there are elements in the array, therefore you have the outer loop.