Gentle Introduction to Programming

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Gentle Introduction to Programming

Assaf ZaritskySummer 2010

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Administration

• August 31 - September 19• 9:00 – 13:30• Mostly at 002דן דויד

• No grading• Web: http://www.cs.tau.ac.il/gip10/

Check what’s new!• My email: [email protected]

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Course Description

This course will provide a gentle introduction to programming

using Scala for highly motivated students with little or no prior experience in programming

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Objective

Bridge the gap for students without prior programming knowledge

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Course Description

Lectures will be interactive featuring in-class exercises with lots of support

You are expected to work hard!

Practical sessions in lab/class

Faculty guests lectures

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Course PlanSession Material

1 Basic concepts in CS and programming, basic Scala

2 Basic Scala (cont.), Functions

3 Recursion

4 Arrays, sorting algorithms

5 Lists

6 Object oriented programming

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Questions?

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Agenda for Today

• Administration• General introduction• The Scala programming language:

• Variables and Types• Compiler, Interpreter• Working environment• Home work• Guest lecture by Ohad Barzilay

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Basic Terms

• Computer Science• Computer• Hardware / Software• Algorithm• Input / Output• Pseudo-Code• Programming Language• Computer Program

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Computer Science

ענף מדעי העוסק בלימוד הבסיס התיאורטי למידע ולחישוביות, והחלתם על מערכות

מחשב

מדעי המחשב אינם עוסקים במחשב יותר משאסטרונומיה עוסקת בטלסקופ", דייקסטרה"

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Computer

מכונה המעבדת נתונים על פי רצף פקודות נתון מראש

מחשב = חומרה + תכנה

מעבד אמצעי פלט

אמצעי קלט

זכרון

עכבר, מקלדת, )(דיסק קשיח

מדפסת, מסך, )(דיסק קשיח

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Algorithm

סדרת פעולות סופית לביצוע משימה מסויימת

Algorithm

Input Output

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לביצוע משימה סופיתסופיתסדרת פעולות אלגוריתם: מסוימת

תרשים זרימה

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Pseudo Code

תיאור מצומצם ולא רשמי לאלגוריתם. מיועד לקריאה של בני אדם

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Example

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Programming Language

Machine-readable artificial language designed to express computations that

can be performed by a computer

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Machine Code (Language)

• Computers understand only machine language• Basically looks like a sequence of 1’s and 0’s• Very inconvenient to work with and non intuitive

• All other computer languages were created for human convenience• The computer does not understand C/C#/Java/Scala• Must be “translated” into machine language

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There are Many Programming Languages

Over 500 different computer languages are listed by Wikipedia

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Language Selection

• Goal• Runtime vs. Development time• Operating systems• Platforms

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Computer Program

מימוש של אלגוריתם באמצעות שפת תכנות

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Computer Program(more technically)

• A sequence of processor instructions designed to achieve a specific purpose

• The instructions are executed sequentially. No instruction is executed before the previous has been completed

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Agenda for Today


• Variables and Types• Operators• Branching and Repetition

• Compiler, Interpreter• Working environment• Home work

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Scala History

• Created by Martin Odersky at EPFL• Released Jan 2004

• Twitter switched large portions of their code to Scala (and intend to convert the rest)• Linkedin use it• Other companies

• Over 4000 downloads per month

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Why Scala?

• Semester A: Scheme• Semester B: Java• Scala language has some features similar to

Scheme and some to Java• Scala is cool!

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Hello World!

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My First Scala Program: Hello World!

Hello.scala

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Memory

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Memory (Cont.)

• The computer memory is composed of a long list of bits

• Bits are grouped into bytes and words

• Every byte is numbered sequentially

• This number is called an address

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Variables and Types

): יחידת מידע המאכסנת ערך variable (משתנה•במהלך ריצת התכנית

ניתן ל"גשת" למשתנה (לשנות או לקבל את ערכו)•ניתן לבצע פעולות חשבוניות (ואחרות) בעזרת •

משתניםשקובע אילו סוגי )type (טיפוסלכל משתנה מוגדר •

ערכים המשתנה יכול להכיל (דוגמאות: מספר שלם, מספר ממשי, תו)

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Define Variables • Use var to declare variables:

var x : Int = 3

var y : Int = 5

var z : Int = x + y

var s1 : String = “Hello World”

define variable

variable name

type valueassignment operator

Variable x “is of type” Int and is assigned the value 3

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Why do We Need Variables?

• Computer programs manipulate data• Data is given as input or calculated throughout

the program• To be later accessed, variables must be

remembered• Thus, variables are stored in the memory• Variable name memory address

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Types

טיפוס של משתנה קובע:• אילו ערכים יכול המשתנה להכיל• מהן הפעולות שניתן לבצע על המשתנה•

שדורש (יחידה בסיסית של זכרון המחשב)מספר הבתים •אחסון של משתנה בזכרון תלוי בטיפוסו

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Some Basic Types

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Why Do We Need Different Types?

• Saving memory

• Execution speed

• Makes compiler “life” easier

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Define Variables • Int:

var x : Int = 5

• Double:var pi : Double = 3.14

• Boolean:var term : Boolean = true

• Char:var c : Char = ‘A’

• String:var st : String = “I want a break!”

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Arithmetic Operators

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Example 1 var a : Int = 3var b: Int = 5var c : Int = a + bprintln(c)c = c * 2println(c)var first : Int = (a + b) * 2var second : Int = a + b * 2println(first)println(second)

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Example 2 // Demonstrate strings additionvar s1 : String = “He”var s2 : String = “llo”var s3 : String = s1 + s2println(s3)var s4 : String = s3 + “ World ”var c : Char = ‘!’println(s4 + 2009 + c)

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Example 3 // Reverse a 3-digits numberprintln(“Enter a 3-digit number”)var num : Int = Console.readInt() // read a number from the user

var ones : Int = num % 10var tens : Int = (num % 100) / 10var hundreds : Int = num / 100

var reverseNum : Int = (ones * 100) + (tens * 10) + hundreds println(“the reverse number is “ + reverseNum)

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Rational Operators

Operator

Name Description

x < y Less than true if x is less than y, otherwise false.

x > y Greater than true if x is greater than y, otherwise false.

x <= y Less than or equal to

true if x is less than or equal to y, otherwise false.

x >= y Greater than or equal to

true if x is greater than or equal to y, otherwise false.

x == y Equal true if x equals y, otherwise false.

x != y Not Equal true if x is not equal to y, otherwise false.

Compares two numbers and returns a Boolean

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Example // Demonstrate rational operatorsprintln(“Enter the first number”)var x : Int = Console.readInt()println(“Enter the second number”)var y : Int = Console.readInt()

println(“x < y is “ + (x < y))println(“x > y is “ + (x > y))println(“x <= y is “ + (x <= y))println(“x >= y is “ + (x >= y))println(“x == y is “ + (x == y))println(“x != y is “ + (x != y))

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Logical Operators Operates on two Booleans and returns a Boolean

Operator

Name Description

x && y And True if both x and y are true, otherwise false.

x || y OrTrue if at least one of x or y are true, otherwise false.

! X Not True if x is false, otherwise false.

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&&, ||, !=

0 1

0 0 0

1 0 1

0 1

0 0 1

1 1 1

0 1

1 0

&&

||!

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Example

// Demonstrate logical operators println(“Enter the first number”)var x : Int = Console.readInt()println(“Enter the second number”)var y : Int = Console.readInt()

println(“(x < 10) && (y < 10) is “ + ((x < 10) && (y < 10)))println(“(x < 10) || (y < 10) is “ + ((x < 10) || (y < 10)))var state : Boolean = ((x < 10) || (y < 10) )println(“state is “ + state)

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All Examples at BasicExamples.scala

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Flow Control

• Usually a program is executed line after line in order

• It is reasonable to expect different execution orders on different inputs• Computer games• Illegal input

• Control structures• if-else• for loop• while loop

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Conditional Statement: if

• Used to execute conditionally a statement (or block of code)

• Syntax: if (expression) statement

• If expression is true, statement is executed

• statement can be replaced by a block of statements, enclosed in curly braces

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if-else Statement

if (expression) statement1

else statement2

• if expression is true, statement1 is executed. • if expression is false, statement2 is executed • both statements can be (and very often are) replaced

by blocks of statements (“compound statements”)

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Agenda for Today


• Variables and Types• Operators


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Compiler

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Interpreter

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Interpreter

• The Read/Evaluate/Print Loop• Read an expression• Compute its value• Print the result• Repeat the above

• The Environment

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Compiler = Clerk"ראש קטן"

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Runtime

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Hello World ;-)

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Agenda for Today




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Working Environment

• Interpreter vs. scripts vs. Eclipse

• Home vs. labs

VS.

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Setting Environment @ Home • Download Java (www.java.com/getjava/ ) • Download Scala (http://www.scala-lang.org/downloads )

• Download Eclipse (http://www.eclipse.org/downloads/ )• Set Scala plugin to Eclipse (https://www.assembla.com/wiki/show/scala-ide/Requirements_and_Installation )

• Start programming

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Download Java http://www.java.com/en/download/index.jsp

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Download Scala http://www.scala-lang.org/downloads

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Download Scala

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Use the Interpreter Type Scala from the command prompt (linux) or using “run” (windows)

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Download Eclipse

http://www.eclipse.org/downloads/

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Set Scala Plugin to Eclipse https://www.assembla.com/wiki/show/scala-ide/Requirements_and_Installation

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Set Scala Plugin to Eclipse (new)

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Set Scala Plugin to Eclipse (new)

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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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Agenda for Today




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Exercise 0

• Write your first “Hello World!” program in Scala:• Use the interpreter• In Eclipse

• Make sure it compiles and executes properly

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Fibonacci

• Fibonacci series0, 1, 1, 2, 3, 5, 8, 13, 21, 34• Definition:

• fib(0) = 1• fib(1) = 1• fib(n) = fib(n-1) + fib(n-2)

en.wikipedia.org/wiki/Fibonacci_number

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סלט פיבונאצ'י

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Exercise 1

• Write a program that receives from the user an integer n > 0 and prints to the screen the n th Fibonacci number

a. Use a “for” loop

b. Use a “while” loop

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Exercise 2

• Write a program that receives from the user two integers 0 < n1 < n2 and prints to the screen all prime numbers between n1 and n2

• Divide the problem to smaller sub-problems:• How would you traverse over all the numbers

between n1 and n2?• How would you be sure that a given number is a

prime?

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Want More Exercises?

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Exercise – Integer Division

• Input:• Two integers – A and B

• Output:• How many times A contains B (it is the result of

the integer division A/B)

• Do not use the operators ‘/’, ‘*’

• Solution:

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Exercise – Power of Two

• Input: integer A

• Output: is there an integer N such that A == 2^N?

• Solution:

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Write a program that prints an upside-down half triangle of *.

The height of the pyramid is the input.

*****

*****

****

*

Exercise – Triangle Printout

Gentle Introduction to Programming

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