CS173: Intro to Computer Science - 2D Arrays
Activity Goals
The goals of this activity are:
- To be able to create, access, and iterate a 2D array
Supplemental Reading
Feel free to visit these resources for supplemental background reading material.
Warmup
What does the
ArrayList.add()
function return? How does this differ from most
String
operations, and why?
The Activity
Directions
Consider the activity models and answer the questions provided. First reflect on these questions on your own briefly, before discussing and comparing your thoughts with your group. Appoint one member of your group to discuss your findings with the class, and the rest of the group should help that member prepare their response. Answer each question individually from the activity, and compare with your group to prepare for our whole-class discussion. After class, think about the questions in the reflective prompt and respond to those individually in your notebook. Report out on areas of disagreement or items for which you and your group identified alternative approaches. Write down and report out questions you encountered along the way for group discussion.
Model 1: 2D Arrays and Traversals
Questions
- How would you describe a 2D array in terms of usual 1D arrays?
- Does the first index indicate the row or the column of the 2D array?
- How might you create a 3-dimensional array?
- Run this code in the Java Visualizer. What is the output?
- Re-draw the arrays
mat1
and mat2
as a square grid.
- Is it possible to re-size these arrays if you need to add additional elements later? If so, how, and if not, why not?
- Develop pseudocode to determine whether a 2D array is a "magic array", in which the sum of each column and row of a square array is the same value. A sample 3x3 magic array is:
[ 4, 9, 2, 3, 5, 7, 8, 1, 6 ]
.
Embedded Code Environment
You can try out some code examples in this embedded development environment! To share this with someone else, first have one member of your group make a small change to the file, then click "Open in Repl.it". Log into your
Repl.it account (or create one if needed), and click the "Share" button at the top right. Note that some embedded Repl.it projects have multiple source files; you can see those by clicking the file icon on the left navigation bar of the embedded code frame. Share the link that opens up with your group members. Remember only to do this for partner/group activities!
Reflective Journal Prompt
- How would you modify the above program to assign values to
mat1
, and then to multiply the two matrices together? To multiply matrices, each cell of the result is equal to the products of each element of the corresponding column of mat1
with each element of the corresponding row of mat2
, added together. A triply-nested loop with a sum is required.
Submission
I encourage you to submit your answers to the questions (and ask your own questions!) using the Class Activity Questions discussion board. You may also respond to questions or comments made by others, or ask follow-up questions there. Answer any reflective prompt questions in the Reflective Journal section of your OneNote Classroom personal section. You can find the link to the class notebook on the syllabus.
For Additional Practice
Feel free to visit these resources for additional practice exercises.