Design Programming DECO2011

Transcription

1 Design Programming DECO2011

2 Rob Saunders web: office: Room 274, Wilkinson Building

3 Data, Variables and Flow Control

4 What is a Variable? Computers can only process one piece of information at a time Variables allow a program to store data at one point and refer back to it later A variable is an item of data with an associated name, or identifier

5 Creating a Variable Before a variable can be used in a program it must be declared Variables are declared by first stating the type of the data, followed by the variable s name int count; This declares a variable named count that stores an integer (a whole number)

6 Variables and Computer Memory All data that a program uses must be stored somewhere in the computer s memory Each piece of data is stored in a specific location, referred to as the address A variable is a name assigned to the address that contains data used by a program

7 Data Types Variables can hold different types of data In Java, variables can hold primitive data types or references to arrays / objects Primitive data types include types for true/false data, characters, whole numbers and real numbers For now, we re just going to look at primitive data types, we ll look at arrays next week and objects later

8 Primitive Data Types boolean truth values true or false char text characters a-z, A-Z, 0-9, etc. byte very small whole numbers -128 to 127 short small whole numbers to int whole numbers to long big whole numbers to float (small) real numbers 1.4e-45 to 3.4e+38 double real numbers 4.9e-324 to 1.8e+308

9 Strongly-Typed Languages Java is a strongly typed language, we have to define what kind of data we want to hold in a variable before it can be used The advantage of a strongly typed language is that we can get the computer to check that we are using a variable correctly before we run the program

10 Weakly Typed Languages JavaScript and ActionScript are weakly typed languages, they do not require variables have their data type defined in advance The advantage of weakly typed languages is that we can program quickly without having to worry about declaring variables first

11 Naming Variables There are some restrictions on variable names: Variable names can only include a limited range of characters: a-z, A-Z, 0-9, _ Variable names cannot contain spaces, the underscore character _ is often used instead of a space Variable names must not start with a number, although they can contain numbers in the middle and at the end

12 Variable Naming Conventions In Java programs, variable names typically begin with a lowercase letter and use a captial letter to start each new word e.g. width, rect4, fillcolour, isfilled Variables that refer to constant data typically use all uppercase letters and underscores between each word e.g. PI, RED, MAX_VALUE

13 Initialising Variables A variable can be declared with no value and then assigned a value later // declare an int named y1 but do not initialise int y1; // assign the value 5 to the variable y1 y1 = 5; A variable can be declared with no value and then assigned a value later // declare an int named y1 initialised to 5 int y1 = 5;

14 Initialising Variables A variable can be initialised with a value, the value of another variable,or by evaluating an expression // declare a char named letter initialised to a char letter = a ; // declare a double named d1 initialised to double d1 = ; // declare a double named d2 initialised to d1 double d2 = d1; // declare a float name z initialised to x * y + 15 float z = x*y f;

15 Scope of Variables The scope of a variable is the part of the code where the variable can be used Variables may have either global or local scope Global variables are ones that can be used anywhere in a program Local variables are ones that can only be used inside a block of code A block of code is defined by the use of curly brackets {... } like the ones used in conditionals, loops and functions

16 Data Hiding If a local variable is declared with the same name as a global variable (or a local variable in a surrounding block) then the program will use the local variable This is why it is important to use good names for variables, if the same variable name is used in multiple scopes it can be difficult tracking which one is being used

17 An Example of Using Global and Local Scopes int x = 20; int s = 15; // Create a global variable x // Create a global variable s if (x > 10) // Use the global variable x { // Start a new code block stroke(s); // Use the global variable s x = 10; // Change the global variable x int s = 255; // Create a local variable s stroke(s); // Use the local variable s } // End the current code block

18 Conditional Statements Conditional statements control which blocks of code execute depending upon the result of some test Tests used by conditional statements always result in a boolean value, i.e. true or false

19 Conditional Tests Conditional tests use the following operators Relational operators > (greater than) < (less than) >= (greater than or equal to) <= (less than or equal to) == (equals)!= (not equals) Logical operators (logical OR) && (logical AND)! (logical NOT)

20 Boolean Logic Named after George Boole Three logical operators; AND, OR and NOT If A is true and B is false then: NOT A is false NOT B is true A AND B is false A AND (NOT B) is true A OR B is true (NOT A) OR B is false The meaning of OR is different from its meaning in English, in Boolean logic A OR B means A is true, or B is true, or both A and B are true

21 Examples of Conditional Tests Simple equality tests: (5 == 6) false (5 == 5) true Relational tests: (5 < 6) true (5 > 5) false (5 <= 5) true Logical tests: (true false) (!false) true true Combined tests:!(15 > 20) true ((5 == 6) && (5 == 5)) false ((5 == 6) (5 == 5)) true

22 Example of a Simple Conditional Statement Print a different message depending on the value of a variable: int x = 5; if (x == 5) { println( x is 5 ); } else { println( x is not 5 ); }

23 Example of Multiple Conditional Statements Print a different message depending on the value of a variable: int x = 5; if (x == 5) { println( x is 5 ); } else if (x == 6) { println( x is 6 ); } else if (x == 7) { println( x is 7 ); } else { println( x is not 5, 6 or 7 ); }

24 Switch Statements The previous example can be rewritten as a switch statement: int x = 5; switch (x) { case 5: println( x is 5 ); break; case 6: println( x is 6 ); break; case 7: println( x is 7 ); break; default: println( x is not 5, 6, or 7 ); }

25 Debugging Conditional Statements What will the following program print out? int x = 5; if (x == 5) { println( x is 5 ); x = 6; } if (x == 6) { println( x is 6 ); x = 5; }

26 Debugging Conditional Statements If we only want to print out one thing we can use an else if statement: int x = 5; if (x == 5) { println( x is 5 ); x = 6; } else if (x == 6) { println( x is 6 ); x = 5; }

27 Randomness Random (stochastic or non-deterministic) processes can be very useful in generating lots of variations of a design We can generate a random number in Processing using the random() function random(value1) random number between 0... value1 random(value1, value2) random number between value1... value2

28 Random Example The following uses random() to generate a number between that is used to determine the background colour float r = random(100); if (r < 50) { background(255, 191, 0); } else { background(191, 0, 255); }

29 Probabilities The previous example tested a random number between to determine if it was less than 50 This is one way to model a probability of something happening 50% of the time e.g. like flipping a coin It is just as simple to model the probability of things happening with different likelihoods

30 Random Example 2 This program draws four rectangles using one of which will be red nostroke(); rectmode(corners); if (random(100) < 25) fill(255,0,0); else fill(255,191,0); rect(0,0,50,50); if (random(100) < 25) fill(255,0,0); else fill(255,191,0); rect(0,50,50,100); if (random(100) < 25) fill(255,0,0); else fill(255,191,0); rect(50,0,100,50); if (random(100) < 25) fill(255,0,0); else fill(255,191,0); rect(50,50,100,100);

31 Colours in Processing Processing supports a three different ways of specifying colours (or colors) Each of these ways of specifying colours is called a colour model The three colour models supported by Processing are: monochrome (greyscale) red, green, blue (RGB) hue, saturation, brightness (HSB)

32 Greyscale Greyscale values range between black and white, or from 0% to 100% brightness By default, Processing allows greyscale values to be specified using values from 0 to = 0% brightness = black 255 = 100% brightness = white Why 255?

33 Red, Green, Blue The red, green, blue colour space, or just RGB for short specifies colours in the way they are produced by computer displays Every pixel in an LCD display is a collection of three tiny lamps, one with a red filter, one with a green filter and one with a blue filter By varying the brightness of the lamps the display can produce a wide range of colours

34 RGB Colour Values By default, Processing supports RGB values between (0, 0, 0) and (255, 255, 255) Processing also RGB values to be specified in hexadecimal, like HTML Processing also allows RGB values to be specified using real numbers More about that in a minute...

35 Hue, Saturation, Brightness Hue, saturation and brightness (HSB) is a colour model that can be much easier to work with than RGB Traditionally, in programs like Photoshop, hue has a range from 0 to 360, saturation and brightness have values between 0% and 100% By default, Processing uses hue saturation and brightness values between 0 and 255

36 Why 255? So why does Processing use values in the range by default? Computers store everything using 1s and 0s, each 1 or 0 in memory is called a bit Computers group bits together into groups of eight called bytes Eight bits, or one byte, can represent the numbers between 0 and 255 So, each value takes exactly one byte to represent if we restrict them to

37 Choosing a Colour Model Processing calls the different colour models color modes Processing allows different color modes to be chosen using the colormode() function colormode(mode); where mode can be either RGB or HSB The greyscale color mode is a special case of the RGB color mode, as we shall see...

38 Specifying Colour Value Ranges It is possible to specify the ranges of colour values when specifying the colour model colormode(mode, range); colormode(mode, range1, range2, range3); where range would apply to all of the RGB or HSB values, and range1, range2, and range3 would apply to R, G, B or H, S, B individually This means that you don t have to use 255!

39 Colour Example 1 nostroke(); colormode(rgb, 100); for(int i = 0; i < 100; i++) { for(int j = 0; j < 100; j++) { stroke(i, j, 0); point(i, j); } }

40 Colour Example 2 nostroke(); colormode(hsb, 100); for(int i = 0; i < 100; i++) { for(int j = 0; j < 100; j++) { stroke(i, j, 100); point(i, j); } }

41 Specifying Colours The background(), fill() and stroke() functions use the current colour model to specify the colour of the window, the interior of shapes and the outline of shapes

42 Specifying Colours Each of these functions can specify the colour to use in different ways, e.g.: fill(value) fill(value, alpha) fill(value1, value2, value3) fill(value1, value2, value3, alpha) fill(color) When only a single value is given, e.g. fill(value) and fill(value, alpha), then the colour being specified is greyscale

43 color It is also possible to specify colours using a special color data type color(gray) color(gray, alpha) color(value1, value2, value3) color(value1, value2, value3, alpha) color(hex) This is very handy if you want to specify a color value and store it in a variable for later use...

44 Colour Example 3 strokeweight(4); rectmode(center); color c1 = color(191, 191, 0); color c2 = color(191, 0, 191); fill(c1); stroke(c2); rect(30, 30, 50, 50); fill(c2); stroke(c1); rect(70, 70, 50, 50);

45 Coursework Assignment

46 Coursework Assignment Create a static sketch Sketch must use random() to produce variations upon a design Sketch should use if-then to produce different designs depending on variables Sketch should use for loops to produce multiple variations in a single window Don t worry we ll cover this next week

47 Coursework Assignment Submission is via your on-line portfolio Submission should include A document describing your design process with references to any interesting examples of similar sketches you liked A series of experimental sketches showing how you developed your idea A final sketch that you developed based upon your experimental sketches

48 REMEMBER IT S WORTH 10%!!!