Lab Assignment 04

Collaboration Policy

The pre-lab requirement must be completed and submitted individually.

The remainder of the lab activity should be completed working in pairs. One person should submit the result, making sure that both partners' names are clearly identified in that submission.

Please make sure you adhere to the policies on academic integrity in this regard.

Pre-Lab Requirement

Read the complete problem description and then determine what the expected output should be if given the following input:

Doubles

As part of an arithmetic competency program, your students will be given randomly generated lists of from 2 to 15 unique positive integers and asked to determine how many items in each list are twice some other item in the same list. You will need a program to help you with the grading. This program should be able to scan the lists and output the correct answer for each one. For example, given the list

1 4 3 2 9 7 18 22

your program should answer 3, as 2 is twice 1, 4 is twice 2, and 18 is twice 9.

The input file will consist of one or more lists of numbers. There will be one list of numbers per line. Each list will contain from 2 to 15 unique positive integers. No integer will be larger than 99. Each line will be terminated with the integer 0, which is not considered part of the list. A line with the single number -1 will mark the end of the file. The example input below shows 3 separate lists. Some lists may not contain any doubles.

The output will consist of one line per input list, containing a count of the items that are double some other item.

Hints

As is often the case, there is more then one approach for solving a problem. There are two distinct strategies to choose from:

1. Use an array of integers (there will be at most 15), and read the input into that array. Then, after doing so, do a second phase where for each value in the data set, you loop through the array looking for twice that value.

2. Represent the data set by using an array of 100 boolean values, perhaps named "mark", so that you set mark[j] = true if j is in the input set and mark[j] = false if j is not in the input. (Note that the problem guarantees that the biggest value can be 99). Next, do a second phase where for each number of the input set, you check whether twice that number also exists in the input set.

Warnings: There are two common pitfalls to avoid

• Don't use illegal array indices. Remember that C++ will not stop you from doing so; instead, it will blindly access a part of memory that is not really the array.

• Make sure to reset your array for each new group. We do not want numbers from one trial to affect the next.

Judge's Data

You can run the automated judge's tests on turing to test the correctness of your program (although you must still formally submit the source code via the course website). If you are working on your own machine (or if you just want to examine the judge's inputs and expected outputs), we provide them here.