Worksheet 7: Selection Sort and Program Proofs Name:
An Active Learning approach to Data Structures using C
1
Worksheet 7: Insertion Sort and Program
Proofs
In preparation: Read Chapter 3 to learn more about debugging, testing and program
proofs.
In Chapter 3 you encountered a number of sorting algorithms. In this lesson you will
investigate yet another algorithm, this one more useful in practical situations than either
bubble or selection sort.
The insertion sort algorithm is most easily described by considering a point in the middle
of execution:
Let p represent an index position in the middle of an array. The invariant you want to
establish is that t this point the elements to the left of p (those with index values smaller
than p) have already been sorted. Those to the right of p are completely unknown. The
immediate task is simply to place the one element that is found at location p so that it,
too, will be part of the sorted portion. To do this, the value at location p is compared to its
neighbor. If it is smaller, it is swapped with its neighbor. It is then compared with the
next element, possibly swapped, and so on.
This process continues until one of two conditions occur. Either a value is found that is
smaller, and so the ordering is established, or the value is swapped clear to the start of the
array.
