© Peter Andreae What is Programming About COMP 102 # T1 Peter Andreae Computer Science Victoria University of Wellington

© Peter Andreae COMP 102 2:2 Menu More course details Strategies for learning in COMP102. Programs and programming languages Object Oriented Programming Reading: Text Book Chapter 1 Announcements: Sign up for a lab session! (Labs start Today) Voting for a Class Rep Put a message about yourself on the forum if you want to be class representative; the class will vote on Monday. Trouble with passwords? Go to school office: CO 358

© Peter Andreae COMP 102 2:3 Lectures vs Textbook Lectures Interactive Multiple media Real time Good for Overview Motivation Problem solving methods Understanding Illustration Textbook One way Visual only Static Re-readable Carefully checked and edited Good for Detailed explanations Lists of facts and rules Careful definitions Large examples How do you use lectures effectively? You didn’t have lectures at school!!

© Peter Andreae COMP 102 2:4 A program is a specification for the behaviour of a computer: What the computer should do when: the program is started the user types something the user clicks with the mouse a message arrives over the network some input from a camera/switch/sensor arrives. …… Responses may be simple or very complex. A program consists of descriptions of responses to events/requests written as instructions in a language the computer can understand: Low level, High level, Specialised What is a Program

© Peter Andreae COMP 102 2:5 Machine & Assembly Language What the computer can understand Different for each computer Very detailed, low-level control of the computer Horrible to read : 000XX00X 0X00XXXX 0XX0X00X 00XXX0X0 00X0X00X X0XX0X0X : copy the contents of memory location 143 into register 1. add the contents of memory location 116 to the contents of register 1. copy the contents of register 1 to memory location 181. : LD d1 143 AD d1 116 ST d1 181 : Pattern of bits controls the switches that operate the CPU

© Peter Andreae COMP 102 2:6 High Level Programming Languages Designed for people to use Designed to be translated into machine language compiled (translated all at once), or interpreted (translated one step at a time), or compiled to an intermediate language, then interpreted (examples at: ) Must be Precise: no ambiguity about what to do Expressive:must be able to specify whatever you want done. Readable: People must be able to read the instructions. Translatable:able to be translated into machine language Concise: not “long-winded” or redundant Smalltalk ML Ada C++ Eiffel Prolog Haskell Miranda Java C# Python Scratch GameMaker Alice FORTRAN LISP Algol COBOL Basic C Pascal Simula Modula PHP Javascript

© Peter Andreae COMP 102 2:7 Specialised language: MazeMouse Writing a program to control a Mouse in a Maze The mouse should get out of the maze No matter what shape the maze is!! The program must cope with “the general case”! Very simple language: Sequence of Forward, Left, and/or Right eg: FLFR What should the mouse do when there’s a space ahead there’s a space only to the left there’s a space only to the right there’s space only to the sides it’s in a dead-end ??

© Peter Andreae COMP 102 2:8 Programming Languages Different languages support different “paradigms”: (ways of designing) imperative, object-oriented, functional, logic programming,... Object Oriented programming languages: Organise program around Classes (types) of objects Each class of objects can perform a particular set of actions Most instructions consist of asking an object to perform one of its actions

© Peter Andreae COMP 102 2:9 Java A high-level Object-Oriented programming language Designed by Sun Microsystems, early-mid 1990's. Widely used in teaching and industry. Related to C++, but simpler. Similar to C#. Good for interactive applications. Extensive libraries of predefined classes to support, UIs, graphics, databases, web applications,... Very portable between kinds of computers.

© Peter Andreae COMP 102 2:10 Constructing Programs Design Edit Test The Design—Edit—Test cycle: Given a task:

© Peter Andreae COMP 102 2:11 Building programs Specification: Work out what you want the program to accomplish Design Work out what the computer must do to accomplish the task Edit Express the design in a programming language instructions for individual steps, structure of the program Test Run the program and see whether it works as intended may need to try it out on lots of different cases.

© Peter Andreae COMP 102 2:12 A program for the Maze Mouse Specification Program to get the mouse out of any maze with a reachable exit (Mouse always starts in the top left corner facing right) Design "make the mouse move into an empty space, When there is a choice, go forward if possible, otherwise to the left" Edit space ahead space only to the left space only to the right space only to the sides dead-end ?? F LF RF LF LLF Program

© Peter Andreae Testing the program (Try it out with the MazeMouse demo) COMP 102 2:13

© Peter Andreae A different task: Specification: Find the average of a sequence of numbers from the user Design: Initialise a count and a running total to 0 Ask the user to enter the numbers Repeat until there are no more numbers: read the next number add it to the total increase the count by 1 If there was at least one number Print out the total / count Otherwise, print a message. COMP 102 2:14

© Peter Andreae COMP 102 2:15 A Java Program import ecs100.*; /** Program to compute the average of a sequence of numbers */ public class MeanFinder { public void findMean () { double total= 0; int count =0; UI.print( "Enter numbers (followed by 'done'): " ); while ( UI.hasNextDouble( ) ) { total = total + UI.nextDouble( ); count = count + 1; } if (count > 0) { UI.printf( "Mean = %5.2f \n", (total/count) ); } else { UI.println( "You entered no numbers"); }

© Peter Andreae COMP 102 2:16 Learning to Program in Java What’s involved? Understand what the computer can do and what the language can specify Problem solving: program design, data structuring, Programming language (Java): syntax and semantics style and common patterns libraries of code written by other people Testing and Debugging (fixing). Common patterns in program design. Important data structures and algorithms.