There are all types of different sorting algorithms, it is a very big topic, especially for beginners. It sounds like may have done bubble sort, the simplest, but least efficient one.
I think merge sort is the best in terms of run time and least confusing. Quick sort is a little better in practice, but difficult to explain. If you know you will only have four variables, you could type it out, but the recursion of merge sort is very nice.
Suppose you have four variables:
a b c d
compare a and b, swap them if b is smaller.
similarly, compare c and d. Suppose b < a, c < d, then we have two sorted lists:
b a
c d
Then just merge them together, i.e. merge sort. Compare b to c, suppose c < b.
Know we know that c is the minimum since c < d, and c < b < a.
c b a
d
We just need to know where d goes. We already know c < d, so we compare b to d. This comparison determines the next smaller number. Suppose b < d. It doesn't help us in placing d, but we know where b goes now, since c < b < a and c < b < d
Finally we have to compare d and a. Suppose d < a. Now we can have a sorted list because we know how everything ranks, c < b < d < a, so:
c b d a
You should always need five comparisons, if you are going to implement merge sort non-recursively, for four elements. I recommend you check out Google, there are plenty of merge sort, and other sort algorithm implementations :D.
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