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Variables

Variables. animation scripting. c sc 233. Lesson Two:. Variables What are they? Declaring and initializing variables Common uses for variables Variables you get “for free” in Processing Aka: Built-in variables Using random values for variables. The basics. The computer has memory

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Variables

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  1. Variables animation scripting csc 233

  2. Lesson Two: • Variables • What are they? • Declaring and initializing variables • Common uses for variables • Variables you get “for free” in Processing • Aka: Built-invariables • Using random values for variables Learning Processing: Slides by Don Smith

  3. The basics • The computer has memory • The computer uses that memory to remember data it needs • A variable is a pointer to a location in the computer’s memory where that data is stored • Variables allow a programmer to save information from one point in the program and refer back to it at a later time • Variables can keep track of information related to shapes, color, size, location • The power of a variable is not that it remembers a value, but that those values can vary and we can alter them. • The value of the variable can change overtime Learning Processing: Slides by Don Smith

  4. What is a variable? • Variable Analogies: • Different sizes • Like a bucket • Like a locker • Like a post-it note • Like a shoe box • Like a dresser drawer • Graph Paper/Spreadsheet • Many ‘storage’ places, all with unique locations (x,y) • In Excel, E3 could be named ‘Billy’s Score’ • Billy’s score can change! A B C D E F 1 2 3 4 5

  5. What is a variability? • Consider this analogy • In a game of Scrabble: • The paper is the “computer memory” • Billy’s score and Jane’s score are the names of variables • The score is a specific Type of data • The score value changes as the game progresses • three ingredients for a variable • Data Type • Name • Value Billy’s score 5 20 53 83 101 Jane’s Score 10 25 47 68 85

  6. What is a variable? • In Algebra: • x = y * z • Named with single letters to represent some number • In Programming: • We use longer, more descriptive names • Variables refer to ‘memory locations’ • Stored in ‘RAM’ • Random Access Memory • Have a ‘size’ • How many bytes of memory ‘wide’ Learning Processing: Slides by Don Smith

  7. Variable Declaration & Initialization • Variables can hold primitive values or references to objects and arrays. For now we will just focus on primitive values • Primitive values are the building blocks of data on the computer and typically involve a singular piece of information, like a number or character. • Before you can use a variable in a program it has to be declared. By declaring the variable you tell the computer the kind of data the variable will contain. This is called the Data type • Give the variable a Unique name. • You can also assign the variable a value, but you do not have to at the time of the declaration. Learning Processing: Slides by Don Smith

  8. Data Types What is a Data Type? • Each type requires a specific amount of storage and the type declaration lets the computer know how much storage to reserve for that variable • ‘Primitive’ types include three main categories • Integers (int)– Whole Numbers (positive and negative), no fractions • Floating point (float) – Numbers with fractional parts and exponents • Characters (char)– One letter that you can type : inside of single quotes • ‘ A’, ‘ B’, ‘C’, ‘a’, ‘b’, ‘1’, ‘2’, ‘3’, ‘%’,’‘&’…. Learning Processing: Slides by Don Smith

  9. All Primitive Types • Integer Types • byte: A very small number (-127 to +128) • short: A small number (-3,2768 to +3,2767) • int: A big number (-2,147,483,648 to +2,147,483,647) • long: A really huge number • Floating Point Types • float: A decimal number such as 3.14159 • double: A huge decimal number used for advanced mathematics • Other Types • boolean: true orfalse (0 or 1) • char: One symbol in single quotes ‘a’

  10. Primitive Type Examples • Integer Types • byte: 123 • short: 1984 • int: 1784523 • long: 234345456789 • Floating Point Types • float: 4.0 • double: 3.14159 • Other Types • boolean: true • char: ‘a’ Learning Processing: Slides by Don Smith

  11. Numeric versus ‘Character’ types • How do you decide if you need a numeric or a character type? • If you plan on doing ‘math’ on the variable, then you MUST use a numeric type • What is the letter ‘a’ times the letter ‘c’? • Notice the single quotes around characters • If you plan on using “Strings” (later), they are just words made up of characters. • “Bob” and “Mary” are Strings (of characters) • Notice the double quotes around strings • What is the string “Bob” times the string “Mary”? Learning Processing: Slides by Don Smith

  12. Variable name • What is in a name • Variables are declared by… • first defining the data type: int (integers), float (floats), char (characters), etc • Second giving the variable a name: • Must be one word (no spaces) • Must start with a letter (not a number) numbers can be used in the name • Must not contain punctuation or special characters • Underscore is allowed in name • it needs to make sense and be descriptive • Example: intcount; data type is Integer, the variable name is count • End the declaration with the semi colon. Learning Processing: Slides by Don Smith

  13. Best Practices for variable names • There are some ‘rules’ and some ‘best practices’ • Rules • Letters, Digits and underscore ( _ ) are OK to use • Cannot start with a digit ( 0,1,…9 ) • Cannot use reserved words • mouseX, int, size.. • Best Practices • Use descriptive names • booleanmoreToDo; • Use ‘camelHump’ notation • Start with lower case • Each new word starts with Upper Case Learning Processing: Slides by Don Smith

  14. Declaring & Initializing Variables • Setting an initial value into the contents of the variable • Pseudocode: Set NumPlayers to 5 • Can be done in two ways: • During Declaration: On one line • int count = 50; // declare and initialize • After declaration: On two lines • int count; // declare the variable • count = 50; // initialize the value • Can also be initialized with a calculation! • int max = 100; • int min = 10; • int count = max – min; // calculation Learning Processing: Slides by Don Smith

  15. Declaration & Initialization examples Type name (optional initialization) ; int count = 0; // Declare an int , initialized to 0 char letter = 'a'; // Declare a char, initialized to 'a' double d = 132.32; // Declare a double, initialized to 132.32 boolean happy = false; // Declare a boolean, initialized to false float x = 4.0; // Declare a float, initialized to 4.0 float y; // Declare a float (no assignment) float z = x * y + 15.0;// Declare a float, initialize it to // x times y plus 15.0. After declaration Assignments: count = 1; letter = ‘b’; happy = true; y = x + 5.2; // Assign the value of x plus 5.2 Learning Processing: Slides by Don Smith

  16. Declaration & Initialization issues • You can only initialize a variable to a value of the same, or compatible type. • Which initializations are compatible? • int count = ‘a’; • char letter = 0; • double deposit = “Fred”; • boolean happy = 1; • float feet = 6; • int inches = feet * 12; • long giant = feet * 3.0; Learning Processing: Slides by Don Smith

  17. Declaration & Initialization issues • If you forget to assign a value to a variable Processing will assign a default value of… • Int = 0 • float = 0.0 Its good to always initialize a value to avoid confusion. Learning Processing: Slides by Don Smith

  18. Where to declare variables • Remember that your code is in ‘blocks’ • Variables can go inside or outside these blocks • For now, we will put them ‘outside’ (before) blocks

  19. Pong Variables • What variables would be required to play? Learning Processing: Slides by Don Smith

  20. Try this:varying variables: • Remember that processing calls draw()in a loop • If you want the variable to change every time: • Declare and initialize it outside of draw()! • Change it inside draw()! Moves as circleX increases 

  21. What happens in example 4.3? • circleXIs initialized to 0 • Used first time draw()is called • ellipse(circleX, circleY, 50,50); • Then circleX = circleX + 1; • Next time draw()is called, circleX is 1 • ellipse(circleX, circleY, 50,50); • Then circleX = circleX + 1; • Next time draw()is called, circleX is 2 • ellipse(circleX, circleY, 50,50); • Then circleX = circleX + 1; • .. Until circleXis over 200, and the circle just moves off the right side of the screen, never to be seen again! • It is often useful to make a ‘table’ of all of the variables that are being changed every time through a ‘loop’ Learning Processing: Slides by Don Smith

  22. Using Many Variables Make things more interesting using more variables! • Declare and initialize them outside of draw()! • Change them inside draw()!

  23. System Variables • Processing provides many ‘built-in’ variables: • These are not for you to play with, but may change! • mouseX , mouseY, pmouseXandpmouseY • width: Width (in pixels) of sketch window • height: Height (in pixels) of sketch window • frameCount: Number of frames processed • frameRate: Rate (per sec.) that frames are processed • key: Most recent key pressed on keyboard • keyCode: Numeric code for which key pressed • mousePressed: True or false (pressed or not?) • mouseButton: Which button (left, right, center) Learning Processing: Slides by Don Smith

  24. Random: Variety is the spice of life • Processing (and all programming languages) provide a way to get a random value when your program runs. • random()is a ‘function’ that returns a float • You can assign this number to a variable and use it! • Some examples: Learning Processing: Slides by Don Smith

  25. casting • (int) • Since random()returns a floating point number and w is an int, we need to change the type from floatto int. • This is called ‘casting’ • random(1,100) ; • (1,100) are ‘parameters’ which tell the random function the range of numbers to return • w will be between 1 and 99 (not quite 100) Learning Processing: Slides by Don Smith

  26. Moving Zoogor your own characterstart simple, then work your way up to moving your entire character across the screen • Use variables and random() to make a Zoog or your character move from upper left to lower right of the screen. • Plan! • Declare variables • Use variables • Use Random Learning Processing: Slides by Don Smith

  27. Summary • Variables have names and types • There are rules and best practices for naming variables • You must declare your variables • Determines the ‘type’, size of storage, and maximum values • You can initialize variables in different ways • Variables have many uses to programmers • processing provides ‘system’ (built-in) variables • You can use random numbers to make your program run differently every time Learning Processing: Slides by Don Smith

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