1 gentle introduction to programming tirgul 1: shell and scala “hands on” in the lab

1

Gentle Introduction to Programming

Tirgul 1: Shell and Scala “hands on” in

the lab

2

Today• Login to your account• Your Account, basic Linux commands• Using the interpreter• Eclipse – “Hello World!”• Understanding compiler messages• Eclipse:

• Command line arguments• Debugger

• Home work – practice Shell commands

3

Today• Login to your account• Your Account, basic Linux commands• Using the interpreter• Eclipse – “Hello World!”• Understanding compiler messages• Eclipse:

• Command line arguments• Debugger

• Home work – practice Shell commands

4

Your Account, Basic Linux Commands

• User’s account: to log in select session: GNOME• Web browser • Open the “system handouts” file from the course’s site (in the session’s section)• Shell / Console

5

Basic Linux Commands

6

Security (chmod)

7

Today• Login to your account• Your Account, basic Linux commands• Using the interpreter• Eclipse – “Hello World!”• Understanding compiler messages• Eclipse:

• Command line arguments• Debugger

• Home work – practice Shell commands

8

Using the Interpreter• Type “scala” from the console• Start trying some basic commands:

• println(“hello world!”)• val x = 5• var y = 1.4

• Define a function that receives two integers and return their sum. Use it on several inputs.

9

Today• Login to your account• Your Account, basic Linux commands• Using the interpreter• Eclipse – “Hello World!”• Understanding compiler messages• Eclipse:

• Command line arguments• Debugger

• Home work – practice Shell commands

10

Eclipse• Type “eclipse35 &” from the console• Use a workspace located on your account• How to solve common technical problems:

• “Clean” your eclipse by removing the .eclipse directory (rm –R .eclipse, from your root)• Start a new workspace / remove the old one

11

Open Eclipse – Set Workspace

12

Open Eclipse

13

Define New Project

14

If you don’t find the Scala new project…

File New Project

15

New Object

16

Write Some Code

17

Run

output

18

Today• Login to your account• Your Account, basic Linux commands• Using the interpreter• Eclipse – “Hello World!”• Understanding compiler messages• Eclipse:

• Command line arguments• Debugger

• Home work – practice Shell commands

19

Understanding Compiler MessagesOpen the interpreter, try the following lines of code, and try to understand what the compiler means, and how to solve it

val x = 5

x = 6

Println(“123”)

val f = (x : Int => x + 1)

if x > f(x) x = 9

val f = (x : int) => x + 1

20

And In Eclipse

• Select and copy a program of your choice to Eclipse• How are compilation errors marked in Eclipse?• Perform compilation errors purposely and see how the compiler’s errors look like:

• Change an upper-case letter to lower case• Remove a closing brackets

• Where are the compiled files?

21

Today• Login to your account• Your Account, basic Linux commands• Using the interpreter• Eclipse – “Hello World!”• Understanding compiler messages• Eclipse:

• Command line arguments• Debugger

• Home work – practice Shell commands

22

Command Line Arguments In Eclipse

23

Command Line Arguments In Eclipse

24

Usage Example

?

Fibonacci.scala

25

Example: Prime

• Write a program that receives from the command line arguments a list of numbers, and prints out for each whether it is prime

• Use the prime code that is published, and wrap it as a function• Notice, that the number of arguments is not known in advance!

26

The Debugger

• Some programs may compile correctly, yet not produce the desirable results

• These programs are valid and correct Scala programs, yet not the programs we meant to write!

• The debugger can be used to follow the program step by step and may help detecting bugs in an already compiled program

27

Debugger – Add Breakpoint

• Right click on the desired line

• “Toggle Breakpoint”

28

Debugger – Start Debugging

breakpoint

debug

29

Debugger – Debug Perspective

30

Debugger – Debugging

Current state

Current location

Back to Scala perspective

31

Today• Login to your account• Your Account, basic Linux commands• Using the interpreter• Eclipse – “Hello World!”• Understanding compiler messages• Eclipse:

• Command line arguments• Debugger

• Home work – practice Shell commands

32

Home Work - Shell