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Introduction to programming - class 1
- 1. Introduction to Programming Class 1 Paul Brebner [email protected] CTO Performance Assurance Pty Ltd
- 2. Notes • Slides, exercises, example programs, etc for an Introductory High School Programming Elective (Years 9 and 10) • No prior experience assumed • Ran for 2 school terms • Required 1 computer per 2 students, a computer and projector for the presenter • Based on the language Processing, www.processing.org • Each class was about 1.5 hours long, included talk and supervised exercises, there was also another 45 minute class per week which was just for practical exercises • Assumes that there is reasonable IT support, that students can download and run things from the internet, and that they can save, share, and load programs
- 3. Who am I? • Computer Scientist – Study of computers and computing – The theory of computing • What is a – Programmer? Software Architect? Software Engineer? IT person? • History of computers (mine)
- 4. Colossus – 70 years old, 1st programmable electronic (valve) computer
- 5. “My” computers • 1978, Burroughs B6700, > $1M • Mainframe Bank computer with “punch cards”
- 6. 2 = Card reader
- 7. First home made • Mini-scamp microcomputer – 1979, $200 • Microprocessor (Computer on a single chip) • 256 Bytes RAM, 1MHz CPU, Input = switches, output = LEDs
- 9. VAX specs • 1MByte RAM (Core memory) • 1MHz CPU, $250,000, lots of circuit boards
- 10. Home designed & made • 1984 • $1,000, 64KBytes RAM • 6809 CPU (2 MHz) • 8” floppy disc • Programmed for – music synthesiser
- 11. Amiga 500 • Game machine! – 1987, $1,000 – 0.5MByte RAM – 7MHz CPU – Colour graphics and sound – Mouse – 3.5 inch floppy disk
- 13. Intel 486 • 1993, homebuilt, 50MHz CPU, $3,000
- 14. Basic computer architecture Address 0 Address 1 Address 2 Address 3 MEMORY CPU BUS Address 100 Address 101 DISPLAY 1 FETCH PC IR 2 DECODE 3 EXECUTE LOADR1 LOADR2 STORE ADDER END Registers R1 R2
- 15. Simulation game • Everyone has a role: – Fetch – Decode – Execute • LOADR1, LOADR2, STORE, ADDER, END – BUS – MEMORY – DISPLAY • Explain Registers and roles
- 16. Simulation • Here’s the program in “binary” – 0101 – 1000 – 0110 – 100 – 1010 – 0101 – 1001 – 1101 – 1010 – 1111
- 17. Simulation: What will it do? Displays two characters... • Here’s the program in “English” (some hidden) – LOADR1 – ? – LOADR2 – 100 – STORE – LOADR1 – ? – INCR2 – STORE – END
- 19. Problem! • Machine code programs – In binary – too hard to read/write – Hard to write large (> 1000 lines?) programs – Only processes binary numbers – what about decimals? text? Images? – Error prone – Not portable – every CPU type has a different instruction set, have to rewrite the program for every CPU type. – Solution • High level programming languages – E.g. Fortran, COBOL, LISP, Prolog, Pascal, C, C++, C#, Java, Javascript, Processing
- 20. High level languages • High level programming language – e.g. Print(“hi”) – Translated (Compiled) into machine code – Or run on a “Virtual machine” – Java “write once, run everywhere” • Runs on a JVM (Java Virtual Machine). • Can run on anything from a mobile phone to a super- computer – “Processing” – a high level graphics language running on top of Java!
- 21. Processing layers • Processing – Runs on • Java – Runs on • JVM – Runs on • Actual CPU
- 22. Lines of Code • How big are programs? 1 LOC – 100M LOC • How many lines of code a day is normal? – 10 LOC a day per programmer (famous figure) – As programs get bigger it gets harder to get them to work correctly • Programming includes other critical tasks – Management (planning for what needs doing when by who) – Specification (what should the program do?) – Design (how should the program do it?) – Programming (writing the program) – Reviewing (reading the program – often someone else’s program – to check it) – Integration (getting your part of the program working with other parts) – Testing (does the program do what is should do? Does it have bugs?) – Debugging (getting rid of the bugs – no program is ever bug free) – Deployment (putting the program where it needs to be to run) – Maintenance (keeping it running, upgrading it) – Retirement (removing the program once it is no longer needed) – Documentation (describing how the program works so someone else can understand it)
- 28. Processing Example: Patterns // Move the mouse around. The faster you go the bigger the ellipse // This is a COMMENT // Primitive processing function: setup() is called once to create screen size and colour void setup() { size(640, 360); background(102); } // Primitive processing function: draw() repeats forever void draw() { variableEllipse(mouseX, mouseY, pmouseX, pmouseY); } // a new function! draws a LARGER ellipse the fasterrrrrrrrrrrrrrrr the mouse speed // speed is computed as the distance between current and previous positions void variableEllipse(int x, int y, int px, int py) { float speed = abs(x-px) + abs(y-py); stroke(speed); // primitive – sets the drawing colour (float type = white to black) ellipse(x, y, speed, speed); // primitive – draws an oval at position x, y, and height and width }