sorting an array of numbers in C

[JVincent08]

Say I have an array (num[3]) that holds 3 numbers. How could I sort those numbers in order from highest to lowest and store them in individual integer variables (highest, middle, lowest) using C? For example:

int num1 = 5;
int num2 = 4;
int num3 = 9;
int num[3];
int highest, middle, lowest;

num[1] = num1;
num[2] = num2;
num[3] = num3;

And sort it so that highest = 9, middle = 5, and lowest = 4.

[Cabhan]

So a few questions:

1) Do you mean to have int pointers, or ints? That is, do you want highest, middle, and lowest to point at the correct spots in the array, or actually hold copies of the numbers?

2) Do you definitely need both the array sorted and the variables holding the numbers?

3) Are there always 3 numbers, or are there more?

The simplest solution would be to run a sorting algorithm on the array. Quicksort is the fastest of these, and though with 3 numbers it doesn't really matter which you choose, it's a good algorithm to know. Once you've run quicksort, you will have a sorted array, so num[0] is the lowest, num[1] is the middle, and num[2] the highest.

[JVincent08]

I guess it doesn't really matter whether I use pointers or actual ints. There are two arrays I need sorting, one will always have 3 numbers, the other will always have 2. I just need a way to refer to the highest, middle, and lowest numbers, whether it be resorting the array or putting them into variables it doesn't matter.

Quicksort is the fastest of these, and though with 3 numbers it doesn't really matter which you choose, it's a good algorithm to know.

Could you give me an example on how to do that?

[drl]

Hi.

There is a good comparison (pun intended) article at Sorting algorithm - Wikipedia, the free encyclopedia including references.

Given the small n, I would do a simple bubble sort for the n=3 case and a simple comparison and possible swap for the n=2 case. The bubble sort is the least efficient sort, but the code is very short and avoids the startup cost of more efficient (but more complex) algorithms like quicksort. My next choice would be insertion sort -- Jon Bentley describes it in 5 lines of code. He also has looked at difficulty of coding. In a small study he did only 10% of professional programmers got a binary search code correct when writing from scratch (Programming Pearls, 2nd edition, page 33 ff), so I lean towards simplicity.

Best wishes ... cheers, drl

[JVincent08]

Ahh thanks guys! The bubble sort does just what I need. I'll learn Quicksort someday when I need it. Thanks again!