Computer Science 340
Programming Languages

Fall 2023, Siena College

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In this lab, we will look at the idea of callback functions. This idea can be used for things such as support of generic searching and sorting routines, or to implement iterator-like functionality over data structures.

You may work alone or in groups of size 2 or 3 on this lab.

Getting Set Up

In Canvas, you will find a link to follow to set up your GitHub repository, which will be named callbacks-lab-yourgitname, for this lab. Only one member of the group should follow the link to set up the repository on GitHub, then others should request a link to be granted write access.

All GitHub repositories must be created with all group members having write access and all group member names specified in the README.md file by 12:50 PM, Tuesday, November 21, 2023. This applies to those who choose to work alone as well!

Java's Arrays.sort Method

Recall Java's Comparator interface, which requires a function compare that is used to compare two instances of a given object type. It returns whether the first is "less than" (return value negative), "equal to" (return value 0), or "greater than" (return value positive) the second.

• Creates 3 arrays of Integer objects containing the numbers

  4, 5, 2, -1, 0, 12

  9, -192, 2

  and

  10, 20, 30, 15, 87, -22, 928, 23, -28, -32, 9, 49152, 2048

• Sorts each array with Arrays.sort() using the natural ordering.
• Sorts each array in decreasing order of the number of times 2 appears in its prime factorization. You will need to write a nontrivial Comparator for this.

Python Lists sort Method

Python lists have extensive functionality, including a sort method. Like Java's Arrays.sort, it takes an optional parameter key= that can be the name of a field of an object to use for the comparison value or the name of a method to call to give a numeric value to the objects that can then be used to order them.

C's qsort Function

The PDF file in the qsort directory of your repository is an excerpt from the classic book The C Programming Language, Second Edition, by Kernighan and Ritchie, Prentice Hall, 1988. That book's Section 5.11 shows you a way you can write a sort function to sort data in multiple ways by specifying a function pointer as one of the parameters to the sort function. This kind of comparator function works similiarly to Java's Compatator.compare methods. In C, we achieve similar functionality but without the formal language or API support.

Make sure you understand how this works, then look at the qsort function provided by the C standard library (man qsort). This works similarly to the one in K&R, but works on an arbitrary array of any data type.

The qsort_examples directory has a program that shows some examples of qsort in action.

Submission

Commit and push!

Grading

This assignment will be graded out of 45 points.