PROGRAMMING. We create identity

Transcription

1 2 PROGRAMMING We create identity

2 TOPICS COVERED Getting Started Setup and draw Variables mousex, mousey other system variables variable declaration types Arithmetic Predefined methods abs, max, delay Topics Look for examples Look at manual Programming as communication Style Naming Comments Constants

3 EXAMPLES Tutorial 1.15 Executed top to bottom. Assignment is not equality Types matter

4 VARIABLE DECLARATION int numsegments; type name use a nice meaningful one

5 VARIABLE DECLARATION int numsegments = 5; intitialisation type name use a nice meaningful one

6 ARITHMETIC x = (3 + x)*(7 + y) + z; y = abs(x - z) % 50; z = (x y)/2; some operations behave differently for different types, e.g. integer division not all operations defined for all types computed top to bottom on left-hand side of = is the variable that gets a new value on the right-hand side of = the expression to compute the new value

7 SCOPE float topx; float topy; void setup(){ topx = width/2; topy = height/2; global variables for shared or persistent data void draw(){ float bottomx; float bottomy; bottomx = topx + width/10; bottomy = topy + height/10; curly brackets define scopes/blocks topx = (topy + 1)% 200; topy = (topy + 1) % 100; local variables for transient data or values

8 EXAMPLE Tutorial 1.16 Global vs local scope Use Global To store data between iterations (persistence) To share data between methods (Note: There are other ways to share) Use local To store values that are used within one method Modern/good programs try to minimize scope

9 COMMENTS Comments can be written in two styles: Single line: float canvolume = 0.355; // Liters in a 12-ounce can The compiler ignores everything after // to the end of line Multiline for longer comments: /* */ This program computes the volume (in liters) of a six-pack of soda cans.

10 CONSTANTS In Processing you can declare CONSTANTS. static final int ITEM_SIZE = 20; Needs initial value Common in Java. Rarely done in Processing. A good idea, also in Processing It tells that this value should not/cannot change It gives an explanatory NAME to a value. Makes code less obscure. Use ALL_CAPS for the name. rectmode CENTER is a constant

11 STYLE Programs must be written for people to read, and only incidentally for machines to execute. - H. Abelson and G. Sussman

12 STYLE Great software, likewise, requires a fanatical devotion to beauty. - Paul Graham

13 STYLE A good program Uses layout to convey the structure. Different components are easily recognized. The code adheres to a given coding guideline. All output is spelled correctly, with a proper layout A poor program The layout is coincidental, It is difficult to identify the structure. Names are cryptic. No discernible effort. Spelling mistakes, poorly formatting of output.

14 STYLE Make yourself familiar with professional style guides Using a good IDE will help to program in style. They will automatically fix many problems in your code.

15 EXAMPLES Check the scope

16 DESCISIONS

17 IFS Within a method all lines are essentially executed one after another. Often you want to make execution conditional. If the x-position is larger than 200 fill the shape blue. If the mouse it pressed, draw eyebrows.

18 IFS Within a method all lines are essentially executed one after another. Often you want to make execution conditional. Or you may want to offer two alternatives, choosing one or the other. If the x-position is larger than 200, fill the shape blue, otherwise, fill it red. If the mouse it pressed, draw eyebrows, otherwise, have the eyes look to the left.

19 IFS Within a method all lines are essentially executed one after another. Often you want to make execution conditional. Or you may want to offer two alternatives, choosing one or the other. Or you may want to offer multiple alternatives, choosing one. If the x-position is larger than 200, fill the shape blue. If y-position smaller the 200, fill it red. Otherwise, fill it green. If the mouse it pressed, draw eyebrows. If mouse pointer is on the left, look left. If mouse pointer is on right, look right. Otherwise, close the eyes.

20 IFS A boolean expression if(condition){ dothis... Executed conditionally

21 IFS A boolean expression if(condition){ dothis... Executed conditionally if(condition){ dothis... else{ dothat... Alternative #1 Alternative #2

22 IFS A boolean expression if(condition){ dothis... Executed conditionally if(conditiona){ dothis... Can be any block of code else if(conditionb){ if(condition){ dothis... else{ dothat... Alternative #1 Alternative #2 dothat... else if(conditionc){ domore... else{ A single line, many lines,... The first satisfied condition determines which branch to execute dosomething... Final else is fall back or default case, in case all conditions fail

23 EXAMPLE Conditional Quadrants conditionals-quadrants Combine ifs to multiple if If increase strokewidth if mousepressed, decrease until otherwise.

24 EXERCISE

25 EXERCISE

26 IFS: NESTED IFS Outer if decides on posx Use nested if to represent tables posy <300 posy>=300 posx <200 blue green 200 <= posx <400 red magenta 400 <= posx cyan yellow if(posx < 200){ if(posy < 300){ fill(0,0,255); else{ fill(0,255,0); else if(posx < 400){ if(posy < 300){ fill(255,0,0); else... else... Inner if decides on posy

27 IFS: UNNECESSARY DUPLICATION Unnecessary Duplication if(mousex>200){ fill(255,0,0); rect(mousex,mousey,10,10); nofill(); else{ fill(0,255,0); ellipse(mousex,mousey,10,10); nofill(); Improved if(mousex>200){ fill(255,0,0); rect(mousex,mousey,10,10); else{ fill(0,255,0); ellipse(mousex,mousey,10,10); nofill();

28 BOOLEAN VARIABLES AND OPERATORS

29 BOOLEAN VARIABLES AND OPERATORS Boolean variables are named after the mathematician George Boole. George Boole ( ), was a pioneer in the study of logic. He invented an algebra based on only two values: TRUE and FALSE.

30 BOOLEAN VARIABLES AND OPERATORS Type boolean The boolean data type represents the Boolean type. Variables of type boolean can hold exactly two values, denoted false and true. These values are not strings. There values are definitely not integers They are special values, just for Boolean variables.

31 BOOLEAN VARIABLES Example of defining a Boolean variable boolean islegalage = false; A Boolean variable named islegalage, initialized to false. It can be set by an intervening statement It can be used later to make a decision

32 BOOLEAN OPERATORS Complex Decisions When you make complex decisions, you often need to combine Boolean values. An operator that combines Boolean conditions is called a Boolean operator. Boolean operators take one or two Boolean values or expressions and combine them into a resultant Boolean value.

33 BOOLEAN OPERATORS Complex Decisions Boolean Algebra allows you to compute with Boolean variables like Algebra with normal variables You have Boolean operations similar to addition and multiplication in normal Algebra. Some common Boolean operators are AND, OR, and NOT.

34 THE BOOLEAN OPERATOR && (AND) Mathematicians use the symbol Boolean AND The Boolean expression a AND b Mathematicians write a b evaluates to true, only if a is true and b is true. Both have to be true. In Processing we use the && operator for AND.

35 THE BOOLEAN OPERATOR && (AND) Example if (sharkfree && sunny) { println( Go swimming! ); You can also combine conditions if ((temperature >=0) && (temperature <=100)) { println( Liquid Water );

36 THE BOOLEAN OPERATOR (OR) Mathematicians use the symbol Boolean or The Boolean expression At least one is true. a or b evaluates to true, if a is true or b is true. Both could be true. In Processing we use the operator for OR. Mathematicians write a b Either Or means exactly one is true. Do NOT confuse OR with EITHER OR!

37 THE BOOLEAN OPERATOR (OR) Example if (sharks rainy) { println( Don t swim! ); Don t swim if there are sharks or if it is rainy. Or both. You can also combine conditions if ((temperature <0) (temperature > 100)) { println( No Liquid Water );

38 THE BOOLEAN OPERATOR (OR) Do you want coffee or tea? Yes! Logic rules! Nerd! You can have too much logic with your coffee (or tea)

39 THE BOOLEAN OPERATOR NOT Mathematicians use the symbol Boolean NOT The Boolean expression NOT a Mathematicians write a evaluates to true, only if a is false. In Processing we use the! operator for NOT.

40 THE BOOLEAN OPERATOR NOT Example if (!sharkfree) { println( Don t swim! ); if (!(temperature >=0)) { println( Freezing ); if it is not shark free don t swim. This is the same as temperature<0

41 THE BOOLEAN OPERATORS Combining operators You can combine different operators. Use parentheses to define the order of evaluation. if (!sharks && (warm sunny)) { println( Go swimming! );

42 1 EXERCISE Given boolean manned = true; boolean aircraft=false; double speed =300; double altitude = 1000; Formula (manned && (speed <1000 aircraft)) (altitude >=1000) sub-formula true or false? (altitude >=1000) (speed <1000) (speed <1000 aircraft) (manned && (speed <1000 aircraft)) (manned && (speed <1000 aircraft)) (altitude >=1000)

43 2 EXERCISE Given boolean manned = false; boolean aircraft=true; double speed =1200; double altitude = 200; Formula (manned && (speed <1000 aircraft)) (altitude >=1000) sub-formula true or false? (altitude >=1000) (speed <1000) (speed <1000 aircraft) (manned && (speed <1000 aircraft)) (manned && (speed <1000 aircraft)) (altitude >=1000)

44 3 EXERCISE Given boolean manned = true; boolean aircraft=true; double speed =100; double altitude = 800; Formula (manned && (speed <1000 aircraft)) (altitude >=1000) sub-formula true or false? (altitude >=1000) (speed <1000) (speed <1000 aircraft) (manned && (speed <1000 aircraft)) (manned && (speed <1000 aircraft)) (altitude >=1000)

45 4 EXERCISE Given boolean green = true; boolean edible=false; double price =3.00; int age = 10; Formula (green && price <10.00) (edible && age >=10) sub-formula true or false? (age >=10) (price <10.00) (green && price <10.00) (edible && age >=10) (green && price <10.00) (edible && age >=10)

46 5 EXERCISE Given boolean green = false; boolean edible=true; double price =12.00; int age = 2; Formula (green && price <10.00) (edible && age >=10) sub-formula true or false? (age >=10) (price <10.00) (green && price <10.00) (edible && age >=10) (green && price <10.00) (edible && age >=10)

47 6 EXERCISE Given boolean green = true; boolean edible=true; double price =1.00; int age = 8; Formula (green && price <10.00) (edible && age >=10) sub-formula true or false? (age >=10) (price <10.00) (green && price <10.00) (edible && age >=10) (green && price <10.00) (edible && age >=10)

48 7 EXERCISE Given boolean hot = true; boolean bread=true; boolean sliced = true; int days = 3; Formula (!hot && bread) && (sliced day >=5) sub-formula true or false?!hot (!hot && bread) (day >=5) (sliced day >=5) (!hot && bread) && (sliced day >=5)

49 8 EXERCISE Given boolean hot = true; boolean bread =false; boolean sliced = true; int days = 5; Formula (!hot && bread) && (sliced day >=5) sub-formula true or false?!hot (!hot && bread) (day >=5) (sliced day >=5) (!hot && bread) && (sliced day >=5)

50 9 EXERCISE Given boolean hot = false; boolean bread=true; boolean sliced = false; int days = 7; Formula (!hot && bread) && (sliced day >=5) sub-formula true or false?!hot (!hot && bread) (day >=5) (sliced day >=5) (!hot && bread) && (sliced day >=5)

51 LOOPS

52 LOOPS: WHILE A while loop has this structure while (condition) { statements The condition is some kind of test (the same as in the if statement) The statements are repeatedly executed while the condition is true. The statements are also called the body of the while. It starts with the keyword while Followed by a condition Followed by one or more statements. The loop stops when the condition is false.

53 LOOPS: WHILE Example

54 LOOPS: INFINITE LOOPS Usually, you want to avoid infinite loops They will make you program crash or freeze. position = 0; while (position <= width) { fill(100); ellipse(position,100,40,40); The variable position is not updated. The condition never false.

55 LOOPS: FORS Often you will need to execute a sequence of statements a given number of times. You could use a while loop for this. counter = 1; // Initialize the counter while (counter <= 10) // Check the counter { println(counter); counter++; // Update the counter

56 LOOPS: FORS The for loop is better than while for doing certain things Things that matter for the loop are all over the place. counter = 1; // Initialize the counter while (counter <= 10) // Check the counter { println(counter); counter++; // Update the counter initialization condition statements update

57 LOOPS: FORS There is a custom made for this sort of processing: for loop The same now as a for loop. for (int counter = 1; counter <= 10; counter++) { println(counter); initialization condition statements update

58 LOOPS: FOR For-loops are used when you want repeat something a set number of times, at regular intervals. for(lines = 0; lines < 20; lines++)... for(xpos = 0; xpos < width; xpos += 10)... Repeat something 20 times. Increment by 10 as long a xpos is smaller than width. for(radius = 100; radius > 0; radius = radius - 20)... Decrement by 20 as long a radius is positive.

59 LOOPS: FOR Examples

60 LOOPS: INFINITE LOOPS You can also have accidentally infinite for-loops They will also make you program crash or freeze. for(int x = 100; x>=0; x +=10){ rect(x,200,5,5); Variable x increases without bounds. Condition never false.

61 PROBLEM SOLVING: HAND-TRACING Hand-tracing is a method of checking your work. To do a hand-trace, write your variables on a sheet of paper and mentally execute each step of your code writing down the values of the variables as they are changed in the code. Keep track where you are in the program, and what values the variables have that way you can also see the history of the values.

62 Line n sum digit comment PROBLEM SOLVING " 0 3 " " 4 " " condition true Consider this example: 1 int n = 738; 2 int sum = 0; 3 int digit; 4 while(n>0){ 5 digit=n % 10; 6 sum = sum + digit; 7 n = n/10; 8 9 println("sum: ",sum); What is the hand trace? What is computed?

63 LOOPS: DRAW Remember: The method draw will be repeated again and again. This is a loop too! Use the draw-loop for animation of different frames or to continuously process user input. Use the for or while-loop to perform multiple similar/same tasks within one frame, or one execution of a method like draw.

64 LOOPS:DRAW Examples drawisaloop Refactor to a for loop. Nice example

65 SEMANTICS

66 SEMANTICS Bad code isn't bad, it s just misunderstood. - Programmers aphorism

67 SEMANTICS Computers are good at following instructions, but not at reading your mind. - D. Knuth

68 SEMANTICS The computing scientist s main challenge is not to get confused by the complexities of his own making. - E. W. Dijkstra

69 SEMANTICS A good program Uses the programming construct correctly and as intended. A poor program It uses programming constructs with no regard for their semantics nor intended use. Every line has a clear purpose and effect. Some lines of code have no clear purpose, or misunderstood effect.