CSE 110 - Lab 1

CSE 110 - Lab 1
Topics
1) Setting up and using an IDE to run a basic Java Program.
2) Problems Solving, Arithmetic Expressions.
3) Getting input from user. Using the Scanner class
Please see the handouts posted under “Useful handouts” if you have not installed the two pieces of
software you need to do your labs and assignments. You will need to download and install: The Java
compiler (known as the JDK) and a Java development environment called Eclipse. Follow these
instructions:
1. Check your system architecture
2. JDK installation
3. Eclipse installation
Some users already have the JDK installed on their computers, because of other software that they use
that is written in Java. If you think this applies to you, you can skip the JDK installation.
Problem Description
Your friend Jenny has a class that gives three tests. She would like you to write a program that will take the three
test grades as input and tell her what her average test grade is. For this Lab you are required to write a program that
will read three test grades from the user and then calculate and print the average of those grades.
Sample Output
Below is an example of what your output should look like when this lab is completed. All text in bold represents
user input. The RED text is your INPUT from the keyboard. You don’t have to round the number at specific
decimal point.
Test Case 1: [90, 91, 92]
Enter the score on the first test: 90
Enter the score on the second test: 91
Enter the score on the third test: 92
Your average score is: 91.0
Test Case 2: [90, 90, 92]
Enter the score on the first test: 90
Enter the score on the second test: 90
Enter the score on the third test: 92
Your average score is: 90.6666
Step 1: Getting Started with Header Documentation
For all assignments and labs in this semester, you should include header documentation in your source code files.
Please put a header at the head of your file as follows, and fill in the information:
/*------------------------------------------------------------
// AUTHOR: YOUR NAME
// FILENAME: TITLE OF THIS SOURCE FILE
// SPECIFICATION: DESCRIPTION OF THIS FILE
// FOR: CSE 110- Lab #1
// TIME SPENT: HOW LONG IT TOOK YOU TO FINISH THIS LAB //--------------------
---------------------------------------*/
Step 2: Setting Up a Scanner for Input
Since you are required to read in the three test grades from the user, you will have to use a Scanner. Follow the
instructions in Chapter 2 to import the Scanner class from the java.util library and create a Scanner object to get
input from the keyboard (System.in).
Step 3: Declaring Variables
Examining the problem, we see that we will need three inputs from the user. We will need variables to hold all of
the inputs. For this Lab, let's assume that all the test grades will be integers. Therefore, we will need three int
variables to hold the three test grades. Remember, if you need more than one variable of the same type, you can
declare them in the same statement separated by commas. For example if we needed two double variables, we could
declare them like:
double var1, var2;
TODO: Declare three int variables to hold the three test grades. Be sure to give them appropriate names like
test1, test2, etc. rather than x, y, z.
Additionally, looking at the problem, we see that we have the number 3 occurring in the problem. Rather than
simply using this number in the program when needed, it is preferable to declare a constant variable to hold the
number so that when it is used in the program, it will be clear what the 3 refers to. Remember to create a constant
you use the keyword final in front of the declaration. Also it is customary to use ALL_CAPS for the name of the
constant. For example if we wanted a constant to hold the value PI, we would declare
final double PI = 3.14159;
TODO: Declare an int constant to hold the value 3, the number of tests. Be sure to give the constant an
appropriate name like NUM_TESTS.
Finally, when looking at a problem you may need variables to hold the solution or some intermediary steps. For this
problem we need to calculate an average. We will need a variable to hold the average. Usually, the average of values
can contain decimal values, so you will need to declare a double variable to hold the average.
TODO: Declare a double variable for an average value
Step 4: Getting the Input
Now that we have the needed variables declared, we are ready to use the Scanner we created to get the input from
the user. Before reading in the input though, it is important to give the user a prompt so the user knows what they are
expected to enter. Then we use the Scanner object with the appropriate method to read in the value and store it in a
variable. For example to prompt and read in the first test score, we would use
Scanner input = new Scanner(System.in);
System.out.print("Enter the score on the first test: "); // prompt
test1 = input.nextInt(); // read in the next integer
where the declared variable test1 will hold the score for the first test and in is the Scanner object.
TODO: Follow the example above, write the prompt and read the input for all THREE tests.
Step 5: Calculate the Average
After reading the three input values from the user, we can use them to calculate the average. To do so we add up all
the values and divide them by the number of tests. Naively, this would be
average = test1 + test2 + test3 / NUM_TESTS;
However, due to operator precedence rules Java will do the division, test3 / NUM_TESTS, before the addition,
which will give the wrong result. To force Java to do the addition first, we have to use parentheses
average = (test1 + test2 + test3) / NUM_TESTS;
This will calculate the average, but there is still a problem. Assume the test grades are 90, 90, and 92, then the
average will be 90.6666, but Java will give the answer as 90 (You should run the program and print the result to
verify). This is because all the variables are integers and so Java does integer division. To force Java to do decimal
division, we have to cast one of the variables to a double. Remember to cast a value to another type you put the type
you want to cast to in parentheses before the value. So, let's cast NUM_TESTS to a double
average = (test1 + test2 + test3) / (double) NUM_TESTS;
Note: Casting sometimes is a risky operation. Please check the textbook for details.
TODO: Calculate the average test score in your code.
Step 6: Display Results
Now that we have calculated the result we need to show it to the user. Use a System.out.println statement to display
the average score to the user. Be sure to have a statement explaining what the number is. That is, don't just print the
number. For example, if we wanted to print the first test score, we would use the following statement:
System.out.println("Your first test score: " + test1);
TODO: Print the result (average score) with helpful message
Step 7: Make sure to upload your Lab1.java
Please submit your Lab1.java ONLY to “Lab 1 Upload Link” in Weekly Labs section. The Lab1.java is in the “src”
folder if you are using Eclipse. Make sure to remove any packaging statement(s) before uploading your file. Do not
include any Eclipse project files. Ask your TA for help, or any questions you may have.