Lab 2: Manipulating and editing files

For the TA

The anwsers to the lab exercises are available in the directory ~/share/Answers (readable only for the grader account).

Tasks:

Help students log in (in case they still have problems)

Show student how to use these concepts and commands:

absoute path
relative path
cat
Output redirection (>)
lpr
mv (rename and move, cover some options, like -i)
cp (copy, cover some options, like -i)
rm (cover some options, like -i)

Show students how to use the gedit editor (see next section in this web page) in the lab
Show student how to use javac and java
(When you show students how to use gedit, write a Java program that reads in a double and prints the sin of the number).
Your job: Help students with the exercise (show then what to do if they get into trouble).

The gedit editor

TA script:

Open terminal
Start gedit:
(Show students the difference between using & and omitting &)

Show student how to:

Insert text
Go to some part of the file (control-I)
Delete text
Replace text (delete and insert)
Search for text (control-F)
Search and replace (control-R)
Save file and quit gedit (control-S, control-Q)
Quit without saving (control-Q)

Make some syntax errors in Hello.java and show students how to run the Java compiler:
Then interpret the error messages (point out the line number in the error message).
Show student how to go to the line in gedit and correct the error.
Then compile again and run the program.
After the intro, let the students do the lab assignment (below in this webpage)

Introduction for students

Objective of this lab:

Today's objective is to:
You can probably do this during the lab time, but if not, it is due by midnight today.

Review:

Shell = the command line interpreter in UNIX
A terminal application is running a shell program.
Editor = a computer application that let you edit computer files.

Review of special directories:

Reading material for this lab
- Reading material:
  You should read the material before coming to the lab. If you have not done so, you will need to read it while the TA is explaining the lab and you can read them after the lab to re-enforce what you have learned.

Preparation

Start a terminal application (see previous lab or ask the TA) and cut-and-paste the following commands (in red) into the terminal:

mkdir ~/cs170/lab2 # Create the lab2 directory inside cs170 cp ~cs170002/share/lab2/* ~/cs170/lab2 # Copy files cd ~/cs170/lab2 # Make lab2 the current directory
ls You should see these 2 files: Convert.java Cylinder.java

If you do not see the files Convert.java and Cylinder.java, ask the TA for help.

Execute the "Convert" Java program

Take a look at the Convert.java program:

UNIX>> cat Convert.java

You should see this output:

import java.util.Scanner; /* This program converts km to miles. */ public class Convert { public static void main(String [] args) { // declaration of the variables double km, miles; // create a Scanner Scanner input; input = new Scanner(System.in); // Enter distance in kilometer System.out.print("Please enter a distance in km: "); km = input.nextDouble(); // Read in input from terminal // and stores it in the variable "km" // Calculate distance in miles miles = 0.62 * km; // print out the result System.out.print(km); System.out.print(" kilometers = "); System.out.print(miles); System.out.println(" miles"); } }

This program reads from the terminal a distance in kilometers and prints the corresponding measure converted in miles.

Compiling the Convert.java program

A Java program must first be translated (= compiled) into executable code using a Java compiler
To translate the Convert.java program, execute this command in the Terminal window:

Now list the directory with the ls command:

UNIX>> ls You should see: Convert.class Convert.java Cylinder.java

Executing the compiled Convert.class program

A compiled Java program is executed using a Java Virtual Machine
To execute the compiled Convert.class program, type this command in the Terminal window:

Sample execution:

UNIX>> java Convert Please enter a distance in km: 2.3 2.3 kilometers = 1.426 miles

Lab Assignment

You should have a copy of the Java program called Cylinder.java in your lab2 directory.
The Cylinder.java file represents the starting point for your program.

Task:

Edit the Cylinder.java file and write the code to compute the volume and the surface area of a cylinder.
Use this command to start the gedit editor to edit your Cylinder.java file:
You should see this window:
Make sure you type the & character at the end of the command line !!!
Ask the TA to help you on how to use gedit if you can't figure things out - the lab is the place to learn to use gedit heads on.

Add the following to the Cylinder.java program: (the tasks are also given inside the Cylinder.java program with comments (//))

Program must Scanner (just like in the Convert.java program) to read from terminal:
- the radius of the cylinder and
- the height of the cylinder.
Note that, both these parameters can be fractional numbers (i.e. double type).
Define the variables needed to store the inputs (radius and height) provided by user.
Use meaningful variable names !
Define a variable of type double called pi and initialize it to 3.14.

Compute the volume and surface area of the cylinder and store the results in variables with meaningful names.

The formulas to compute the volume and the surface area of a cylinder are as follows:
where baseArea = radius * radius * pi.

Using System.out.println() to print out the volume and the surface area.

What you must do to finish the lab:

In the gedit window, enter all the necessary Java statements
When finish, click Save
After saving the program, enter this command in the terminal window to compile the program:
If the compiler reports some errors, you must fix them using gedit. Save the changes and compile again until there are no errors.
After successfully compiling the program, enter this command in the terminal window to run the program:
The program will prompt you for 2 inputs and then prints the volume and surface area
Example of an interaction with the program (you type in the text in red):

Turnin
- When you are done, turnin lab 2 using this command:
  This makes a copy of your file (Cylinder.java) in the grader's account.
  Your turnin is successful when you see this message:
  For the Lead TA:
Additional exercise: if you are serious about becoming a Computer Science major, do the additional exercise to hone your editing and programming skills.

Additional lab exercise

Write a Java program that reads in an integer n < 10000 (= read in an integer value and store it in the variable n) and then computes the sum of the digits in the number.
Note:

Hints:

n % 10 will return the last digit in the number n

Example:

if n = 12345 then n % 10 returns 5

n / 10 will return the number n without the last digit

Example:

if n = 12345 then n / 10 returns 1234

You don't need to turn in the additional lab exercise, but you can get help from the TA to work on the problem.