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

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Gentle Introduction to Programming

Tirgul 1: Shell and Scala “hands on” in

the lab

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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

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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

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Basic Linux Commands

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Security (chmod)

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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.

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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

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Open Eclipse – Set Workspace

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Open Eclipse

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Define New Project

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If you don’t find the Scala new project…

File New Project

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New Object

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Write Some Code

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Run

output

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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

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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?

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Command Line Arguments In Eclipse

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Command Line Arguments In Eclipse

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Usage Example

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Fibonacci.scala

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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!

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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

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Debugger – Add Breakpoint

• Right click on the desired line

• “Toggle Breakpoint”

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Debugger – Start Debugging

breakpoint

debug

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Debugger – Debug Perspective

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Debugger – Debugging

Current state

Current location

Back to Scala perspective

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Home Work - Shell

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

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