Computer Science II

Lab 2.0 - Conditionals & Loops

School of Computing
College of Engineering
University of Nebraska-Lincoln
University of Nebraska-Omaha

An introduction to using conditionals and loops in the Java programming language. A separate folder containing a Python version of this lab is included for the honors section.

Overview

Resources

Prior to lab you should read/review the following resources.

if-else tutorial: http://download.oracle.com/javase/tutorial/java/nutsandbolts/if.html
for loop tutorial: http://download.oracle.com/javase/tutorial/java/nutsandbolts/for.html
while loop tutorial: http://download.oracle.com/javase/tutorial/java/nutsandbolts/while.html

Lab Objectives & Topics

Following the lab, you should be able to:

Use if-else statements to control the logical flow of the program.
Use for and while loops to implement repetition statements in a program.
Write complex programs that require conditional logical statements and loops.

Peer Programming Pair-Up

To encourage collaboration and a team environment, labs will be structured in a pair programming setup. At the start of each lab, you may be randomly paired up with another student by a lab instructor. One of you will be designated the driver and the other the navigator.

The navigator will be responsible for reading the instructions and telling the driver what is to be done. The driver will be in charge of the keyboard and workstation. Both driver and navigator are responsible for suggesting fixes and solutions together. Neither the navigator nor the driver is "in charge."
Beyond your immediate pairing, you are encouraged to help and interact and with other pairs in the lab.

Each week you should try to alternate: if you were a driver last week, be a navigator next, etc. Resolve any issues (you were both drivers last week) within your pair. Ask the lab instructor to resolve issues only when you cannot come to a consensus.

Because of the peer programming setup of labs, it is absolutely essential that you complete any pre-lab activities and familiarize yourself with the handouts prior to coming to lab. Failure to do so will negatively impact your ability to collaborate and work with others which may mean that you will not be able to complete the lab.

1. Getting Started

Clone this project code for this lab from GitHub in Eclipse using the URL: https://github.com/cbourke/CSCE156-Lab02. Refer to Lab 1.0 for instructions on how to clone a project from GitHub.

For those with prior Java experience, do the PHP version of this lab. For those without prior Java experience, do the Java version.

2. Conditionals & Loops

Java provides standard control structures for conditionals and repetition. Specifically, Java provides the usual if-else statements as well as for and while loops. The syntax for these control structures should look familiar. Some examples:

if(x > 0) {
  //DO SOMETHING
} else if(x < 0) {
  //DO SOMETHING ELSE
} else {
  //OTHERWISE
}

for(int i=0; i<n; i++) {
  //DO SOMETHING
}

int i = 0;
while(i < n) {
  //DO SOMETHING
  i++;
}

In addition, Java provides a foreach-loop, also referred to as an enhanced for-loop, for iterating over collections or elements in an array. This feature is mostly for convenience. The following example demonstrates how to use this loop.

String arr[] = new String[10];
...
for(String s : arr) {
  System.out.println(s); 
}

An enhanced for-loop can be used for Set and List collections.

3. Activities

3.1 Sum of Natural Numbers

Natural numbers are the usual counting numbers; 1, 2, 3, ... In this exercise you will write several loops to compute the sum of natural numbers 1 thru n where n is read from the command line. You will also write an enhanced for-loop to iterate over an array and process data.

Open the Natural.java source file. The code to read in n has been provided for you. An array mapping integer values 1 thru 10 to text values has also been created for you.
Write a for-loop and a while-loop in the relevant methods to compute the sum of natural numbers 1 thru n and return the result. In the main method call your methods and output the result.
Write a an enhanced for-loop to iterate over the elements of the zeroToTen array. As you iterate over the elements, concatenate each string, delimiting each word with a plus sign and the result at the end of the loop. Your result should look something like the following:

zero + one + two + three + four + five + six + seven + eight + nine + ten = 55

3.2 Child Tax Credit

When filing for federal taxes, a credit is given to tax payers with dependent children according to the following rules. The first (not necessarily the oldest) dependent child younger than 18 is worth a $1,000.00 credit. Each dependent child younger than 18 after the first child is worth a $500 tax credit each. You will complete a Java program to output a table of dependent children, how much each contributes to a tax credit, and a total child tax credit. Your table should look something like the following.

Child           Amount
Tommy (14)      $1000.00
Richard (12)    $500.00
Harold (21)     $0.00
Total Credit:   $1500.00

Open the Child.java and ChildCredit.java source files
The Child class has already been implemented for you. Note how the Child class is used. Several instances of children have been created and placed into a List.

Similar to an array, a List stores elements using 0-indexing. Each one can be accessed using the get method. For example, kids.get(i) gets the i-th kid. You could also use an enhanced for loop to iterate over the elements in the List.
Implement the produceReport method to compute the child tax credit(s) and output a table similar to the one above. Your method should return the grand total of the credit.

Each child is an instance of the Child class. Each instance has its own variables so that each child can be a different age. To get a particular child’s age, you can use a getter method. For example, to get the age of tom you can use the syntax, tom.getAge()

4. Testing, Submitting & Grading

Test your programs using the provided JUnit test suite(s). Fix any errors and completely debug your programs.
Submit the following files:
- Natural.java
- ChildCredit.java
Run the grader and verify the output to complete your lab.

Advanced Activity (Optional)

Use the String.format() method to reformat the output of the Child Tax Credit program to print every piece of data in its own column.