Programming and Problem Solving Introduction to the Course Spring - - PowerPoint PPT Presentation

Dennis Komm

Programming and Problem Solving

Introduction to the Course

Spring 2019 – February 18, 2019

Welcome to the Course

Material

Lecture website

http://lec.inf.ethz.ch/ppl

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 1 / 52

The Team

Lecturer Dennis Komm Assistants Moritz Hoffmann Jean Kaufmann Angela Rellstab

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 2 / 52

Programming and Problem Solving

In this course, you will learn programming in Java Software development is a craftmanship Just like learning to play an instrument

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 3 / 52

Programming and Problem Solving

In this course, you will learn programming in Java Software development is a craftmanship Just like learning to play an instrument Problem: So far, no one became a pianist simply by listening

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 3 / 52

Programming and Problem Solving

In this course, you will learn programming in Java Software development is a craftmanship Just like learning to play an instrument Problem: So far, no one became a pianist simply by listening Therefore, this course gives you many opportunities to exercise Use them!

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 3 / 52

Programming and Problem Solving

In this course, you will learn problem solving with appropriate algorithms and data structures Language-independent basic knowledge Analogous to rhythm theory, musical scale, and reading notes

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 4 / 52

Programming and Problem Solving

In this course, you will learn problem solving with appropriate algorithms and data structures Language-independent basic knowledge Analogous to rhythm theory, musical scale, and reading notes Problem: This is only limited fun without a musical instrument

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 4 / 52

Programming and Problem Solving

In this course, you will learn problem solving with appropriate algorithms and data structures Language-independent basic knowledge Analogous to rhythm theory, musical scale, and reading notes Problem: This is only limited fun without a musical instrument Therefore, we combine all this with learning to program in Java

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 4 / 52

Goal of Today’s Lecture

Introduction / repetition computer model and algorithms General information about the lecture The first Java program

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 5 / 52

Introduction to the Course

Computer Model and Algorithms

Computer – Concept

What do computers have to be able to do to compute? Does it have to be able to multiply? Is it not sufficient to be able to add?

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 6 / 52

Computer – Concept

What do computers have to be able to do to compute? Does it have to be able to multiply? Is it not sufficient to be able to add? Turing Machine [Alan Turing, 1936] Finite number of states Memory consisting of arbitrarily many cells Pointer to current cell Pointer can change cell’s content and move left or right

Alan Turing [Wikimedia] Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 6 / 52

Computer – Implementation

Analytical Engine – Charles Babbage (1837) Z1 – Konrad Zuse (1938) ENIAC – John von Neumann (1945)

Charles Babbage [Wikimedia] Konrad Zuse [Wikimedia] John von Neumann [Wikimedia] Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 7 / 52

Computer – Implementation

Components of von Neumann Architecture Memory for programs und data, random access memory (RAM) Processor (CPU) for processing of programs and data I/O components to communicate with periphery Processor – CPU

Arithemtic unit ALU Control unit

BUS Memory In-/Output

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 8 / 52

Memory for Program and Data

Sequence of bits Program data: Values of all bits Combination of bits to memory cells (8 bits = 1 byte)

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 9 / 52

Memory for Program and Data

Sequence of bits Program data: Values of all bits Combination of bits to memory cells (8 bits = 1 byte) Every memory cell has an address Random access: Access time (almost) independent of address 0 1 0 0 1 1 0 1 0 0 1 0 1 1 1 0 Address: 17 Address: 18

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 9 / 52

Algorithm: Central Notion of Computer Science

Algorithm Method for step-by-step solution of a problem

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 10 / 52

Algorithm: Central Notion of Computer Science

Algorithm Method for step-by-step solution of a problem Execution does not require intellect, only accuracy

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 10 / 52

Algorithm: Central Notion of Computer Science

Algorithm Method for step-by-step solution of a problem Execution does not require intellect, only accuracy after Muhammed al-Chwarizmi; author of a Persian math book (around 825)

"‘Dixit algorizmi. . . "’ Latin translation [Wikimedia] Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 10 / 52

“The Oldest (Known) Non-Trivial Algorithm”

Euclid’s Algorithm

from Euclid’s Elements, 300 BC

Input: integers a > 0, b > 0 Output: gcd of a and b

Input: a and b while b = 0 if a > b then a = a − b else b = b − a Output: a

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 11 / 52

“The Oldest (Known) Non-Trivial Algorithm”

Euclid’s Algorithm

from Euclid’s Elements, 300 BC

Input: integers a > 0, b > 0 Output: gcd of a and b

Input: a and b while b = 0 if a > b then a = a − b else b = b − a Output: a

a b

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 11 / 52

“The Oldest (Known) Non-Trivial Algorithm”

Euclid’s Algorithm

from Euclid’s Elements, 300 BC

Input: integers a > 0, b > 0 Output: gcd of a and b

Input: a and b while b = 0 if a > b then a = a − b else b = b − a Output: a

a b a b

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 11 / 52

“The Oldest (Known) Non-Trivial Algorithm”

Euclid’s Algorithm

from Euclid’s Elements, 300 BC

Input: integers a > 0, b > 0 Output: gcd of a and b

Input: a and b while b = 0 if a > b then a = a − b else b = b − a Output: a

a b a b a b

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 11 / 52

“The Oldest (Known) Non-Trivial Algorithm”

Euclid’s Algorithm

from Euclid’s Elements, 300 BC

Input: integers a > 0, b > 0 Output: gcd of a and b

Input: a and b while b = 0 if a > b then a = a − b else b = b − a Output: a

a b a b a b a b

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 11 / 52

Computing Speed

In the avergage time my voice travels to you. . .

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 12 / 52

Computing Speed

In the avergage time my voice travels to you. . . 30 m a desktop computer executes more than

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 12 / 52

Computing Speed

In the avergage time my voice travels to you. . . 30 m = more than 100 000 000 instructions a desktop computer executes more than 100 million instructions

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 12 / 52

Java

Java is based on a virtual machine (with von Neumann architecture)

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 13 / 52

Java

Java is based on a virtual machine (with von Neumann architecture)

program code is tranlated to intermediate code

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 13 / 52

Java

Java is based on a virtual machine (with von Neumann architecture)

program code is tranlated to intermediate code Intermediate code runs a simulated environment, interpreted through special interpreter

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 13 / 52

Java

Java is based on a virtual machine (with von Neumann architecture)

program code is tranlated to intermediate code Intermediate code runs a simulated environment, interpreted through special interpreter Optimization: Just-in-Time (JIT) compilation of frequently used code: virtual machine ➯ physical machine

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 13 / 52

Java

Java is based on a virtual machine (with von Neumann architecture)

program code is tranlated to intermediate code Intermediate code runs a simulated environment, interpreted through special interpreter Optimization: Just-in-Time (JIT) compilation of frequently used code: virtual machine ➯ physical machine

Implication and declared goal of the Java developers: portability

“write once – run anywhere”

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 13 / 52

Introduction to the Course

Project

Ready, Set, Go!

You have seven weeks to complete a non-trivial project After the first few weeks you will already know the basic concepts, to implement the project

1 2 3 4 5 6 7 learning curve

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 14 / 52

Ready, Set, Go!

You have seven weeks to complete a non-trivial project After the first few weeks you will already know the basic concepts, to implement the project

1 2 3 4 5 6 7 learning curve project

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 14 / 52

Java Tutorial

In the first weeks, you independently work on our Java tutorial Easy introduction to Java, no previous knowledge necessary Time needed: roughly two hours In the second week, there will be a self-assessment

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 15 / 52

Java Tutorial

In the first weeks, you independently work on our Java tutorial Easy introduction to Java, no previous knowledge necessary Time needed: roughly two hours In the second week, there will be a self-assessment

➯ This time is well invested

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 15 / 52

Java Tutorial

In the first weeks, you independently work on our Java tutorial Easy introduction to Java, no previous knowledge necessary Time needed: roughly two hours In the second week, there will be a self-assessment

➯ This time is well invested

Tutorial website

https://frontend-1.et.ethz.ch/sc/WKrEKYAuHvaeTqLzr

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 15 / 52

Project

You choose a project from a list of predefined projects The project is worked on independently Pattern: Data ➯ read in ➯ process ➯ output Information is continuously updated on course website Exericse: Wednesday, 17–18, HG 26.5 (right after the lecture) Supervised by Moritz Hoffmann, CAB F 69 (moritz.hoffmann@inf.ethz.ch), office hours: Monday, 15–17

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 16 / 52

Project – Team Work is Key

You work in teams of two Both partners contribute provably half Projects are graded per team

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 17 / 52

Project – Team Work is Key

You work in teams of two Both partners contribute provably half Projects are graded per team

➯ Contact us as soon as there are any problems or

disagreements

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 17 / 52

Project – Milestones

Milestones have to be complied with Compliance with the milestone will be part of the grade Every milestone corresponds to some output (document or code)

Week 2

Team assembled Project chosen Tools installed First GIT commit

Week 3

Project plan handed in Solution design fixed

Week 6

All features ready Test plan done

Week 7

Handing in all materials Presentation

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Graded Semester Performance

Presentation of the project on April 3 and 10 Duration: Around 10 minutes, depending on the number of projects handed in Handing in all materials All milestones have to be complied with

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Discussion Platform

You can sign in to our Slack forum

https://bit.ly/2UXaWzg

General discussion of course Search for team partners . . .

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Introduction to Java

Programming Tools

Editor: Program to modify, edit and store Java program texts

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 21 / 52

Programming Tools

Editor: Program to modify, edit and store Java program texts Compiler: Program to translate a program text into machine language (intermediate code, respectively)

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 21 / 52

Programming Tools

Editor: Program to modify, edit and store Java program texts Compiler: Program to translate a program text into machine language (intermediate code, respectively) Computer: Machine to execute machine language programs

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 21 / 52

Programming Tools

Editor: Program to modify, edit and store Java program texts Compiler: Program to translate a program text into machine language (intermediate code, respectively) Computer: Machine to execute machine language programs Operating System: Program to organize all procedures such as file handling, editing, compiling, and program execution

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 21 / 52

English vs. Programming Language

English “Science is what we understand well enough to explain to a computer. Art is everything else we do. ”

DONALD KNUTH

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 22 / 52

English vs. Programming Language

English “Science is what we understand well enough to explain to a computer. Art is everything else we do. ”

DONALD KNUTH

Java / C / C++

// computation int b = a * a; // b = a^2 b = b * b; // b = a^4

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 22 / 52

Syntax and Semantics

Like our language, programs have to be formed according to certain rules

Syntax: Connection rules for elementary symbols (characters) Semantics: Interpretation rules for connected symbols

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 23 / 52

Syntax and Semantics

Like our language, programs have to be formed according to certain rules

Syntax: Connection rules for elementary symbols (characters) Semantics: Interpretation rules for connected symbols

Corresponding rules for a computer program are simpler but also more strict because computers are relatively stupid

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 23 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast.

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast.

Syntactically and semantically correct

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat.

Syntactically and semantically correct

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat.

Syntactically and semantically correct Syntax error: word building

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is.

Syntactically and semantically correct Syntax error: word building

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is.

Syntactically and semantically correct Syntax error: word building Syntax error: word order

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking my dog and my cat

Syntactically and semantically correct Syntax error: word building Syntax error: word order

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking, my dog, and my cat.

Syntactically and semantically correct Syntax error: word building Syntax error: word order Syntax error: missing punctuation marks

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking my dog and my cat She is not tall and red-haired.

Syntactically and semantically correct Syntax error: word building Syntax error: word order Syntax error: missing punctuation marks

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking my dog and my cat She is not tall and red-haired.

Syntactically and semantically correct Syntax error: word building Syntax error: word order Syntax error: missing punctuation marks Syntactically correct, but ambiguous [no analogon]

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking my dog and my cat She is not tall and red-haired. I own an red car.

Syntactically and semantically correct Syntax error: word building Syntax error: word order Syntax error: missing punctuation marks Syntactically correct, but ambiguous [no analogon]

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking my dog and my cat She is not tall and red-haired. I own an red car.

Syntactically and semantically correct Syntax error: word building Syntax error: word order Syntax error: missing punctuation marks Syntactically correct, but ambiguous [no analogon] Syntactically correct, but gramatically and semanti- cally wrong: wrong article [type error]

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking my dog and my cat She is not tall and red-haired. I own an red car. The bike gallops fast.

Syntactically and semantically correct Syntax error: word building Syntax error: word order Syntax error: missing punctuation marks Syntactically correct, but ambiguous [no analogon] Syntactically correct, but gramatically and semanti- cally wrong: wrong article [type error]

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking my dog and my cat She is not tall and red-haired. I own an red car. The bike gallops fast.

Syntactically and semantically correct Syntax error: word building Syntax error: word order Syntax error: missing punctuation marks Syntactically correct, but ambiguous [no analogon] Syntactically correct, but gramatically and semanti- cally wrong: wrong article [type error] Syntactically and gramatically correct, but semanti- cally wrong [run-time error]

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking my dog and my cat She is not tall and red-haired. I own an red car. The bike gallops fast. We saw her duck.

Syntactically and semantically correct Syntax error: word building Syntax error: word order Syntax error: missing punctuation marks Syntactically correct, but ambiguous [no analogon] Syntactically correct, but gramatically and semanti- cally wrong: wrong article [type error] Syntactically and gramatically correct, but semanti- cally wrong [run-time error]

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Kinds of Errors Illustrated with English Language

The car drove too fast. Thecar drove too fsat. Red the car is. I find inspiration in cooking my dog and my cat She is not tall and red-haired. I own an red car. The bike gallops fast. We saw her duck.

Syntactically and semantically correct Syntax error: word building Syntax error: word order Syntax error: missing punctuation marks Syntactically correct, but ambiguous [no analogon] Syntactically correct, but gramatically and semanti- cally wrong: wrong article [type error] Syntactically and gramatically correct, but semanti- cally wrong [run-time error] Syntactically and sematically correct, but ambiguous [no analogon]

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 24 / 52

Introduction to Java

A First Java Program

A First Java Program

// input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b);

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 25 / 52

A First Java Program

public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b); }

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 25 / 52

A First Java Program

public class Main { public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b); } }

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 25 / 52

A First Java Program

public class Main { public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b); } } Method: named sequence of statements Class: a program

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 25 / 52

Behavior of a Program

At compile time Program accepted by the compiler (syntactically correct) Compiler error

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 27 / 52

Behavior of a Program

At compile time Program accepted by the compiler (syntactically correct) Compiler error During runtime correct result incorrect result program crashes program does not terminate (endless loop)

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 27 / 52

Comments

public class Main { public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b * b, i.e., a^8 Out.println(a + "^8 = " + b * b); } }

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 28 / 52

Comments

public class Main { public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b * b, i.e., a^8 Out.println(a + "^8 = " + b * b); } } Comments

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 28 / 52

Comments and Layout

The compiler does not care. . .

public class Main{public static void main(String[] args){Out.print ("Compute a^8 for a= ?");int a;a = In.readInt();int b = a*a;b = b * b;Out.println(a + "^8 = " + b * b);}}

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 30 / 52

Comments and Layout

The compiler does not care. . .

public class Main{public static void main(String[] args){Out.print ("Compute a^8 for a= ?");int a;a = In.readInt();int b = a*a;b = b * b;Out.println(a + "^8 = " + b * b);}}

. . . but we do

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 30 / 52

Introduction to Java

Statements

Statements

public class Main { public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b); } }

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 31 / 52

Statements

public class Main { public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b); } } Expression statements

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 31 / 52

Statements – Values and Effects

public class Main { public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b); } }

Effect: Output of the string Compute ... Effect: Input of number and store it in a Effect: Store the computed value of a*a in b Effect: Store the computed value of b*b in b Effect: Output of the value of a, the string ˆ8 = , and the calculated value of b*b

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 35 / 52

Introduction to Java

Declaration

Variable Definitions

public class Main { public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b); } }

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 37 / 52

Variable Definitions

public class Main { public static void main(String[] args) { // input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b); } } Declaration statement Type names

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 37 / 52

Introduction to Java

Variables and Objects

Variables

Variables represent (varying) values have

name type value address

are “visible” in the program context

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 42 / 52

Variables

Variables represent (varying) values have

name type value address

are “visible” in the program context Example

int a; defines a variable with

name: a type: int value: (initially) undefined address: determined by compiler

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 42 / 52

Objects

Objects represent values in main memory have type, address and value (memory content at the address) can be named . . . . . . but also anonymous

Remark A program has a fixed number of variables. In order to be able to deal with a variable number of values, it requires “anonymous” addresses that can be addressed via temporary names.

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 43 / 52

Introduction to Java

Expressions

Expressions

Expressions represent computations

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 45 / 52

Expressions

Expressions represent computations are either primary (b)

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 45 / 52

Expressions

Expressions represent computations are either primary (b)

• r composed (b * b). . .

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 45 / 52

Expressions

Expressions represent computations are either primary (b)

• r composed (b * b). . .

. . . from different expressions by operators

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 45 / 52

Expressions

// input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b * b, i.e., a^8 Out.println(a + "^8 = " + b * b );

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 46 / 52

Expressions

// input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b * b, i.e., a^8 Out.println(a + "^8 = " + b * b ); Variable name, primary expression Variable name, primary expression

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 46 / 52

Expressions

// input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b * b, i.e., a^8 Out.println(a + "^8 = " + b * b ); Composite expression

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 46 / 52

Introduction to Java

Operators and Operands

Operators and Operands

// input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b );

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 49 / 52

Operators and Operands

// input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b ); Left operand (variable) Right operand (expression)

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 49 / 52

Operators and Operands

// input Out.print("Compute a^8 for a= ?"); int a; a = In.readInt(); // computation int b = a * a; // b = a^2 b = b * b; // b = a^4 // output b*b, i.e., a^8 Out.println(a + "^8 = " + b * b ); Left operand (variable) Right operand (expression) Assignment operator Multiplication operator

Programming and Problem Solving – Introduction to the Course Spring 2019 Dennis Komm 49 / 52

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