Pick a number. Conditionals. Boolean Logic Relational Expressions Logical Operators Numerical Representation Binary. CS Conditionals 1

Transcription

1 Conditionals Boolean Logic Relational Expressions Logical Operators Numerical Representation Binary CS Conditionals 1 Pick a number CS Conditionals 2

2 Boolean Expressions An expression that evaluates to true or false. Relational boolean expressions: - is your number greater than 50? - is your number less than 40? - is your number equal to 73? - is your number greater than or equal to 75? - is your number less than or equal to 37? - is your number not equal to 99? CS Conditionals 3 Relational Operators is your number greater than 50? number > 50 is your number less than 40? number < 40 is your number equal to 73? number == 50 is your number greater than or equal to 75? number >= 75 is your number less than or equal to 37? number <= 37 is your number not equal to 99? number!= 99 CS Conditionals 4

3 (demo) // my number to guess int number = 73; // a relational expression used to guess my number println(number > 50); CS Conditionals 5 True or False? int a = 8; int b = 5; 6 < a a / 2 > 6 a * 5 == 8 * b b!= 5 A. true B. false C. neither true or false CS Conditionals 6

4 Conditional Statement if a boolean expression is true, then execute a block of code boolean expression code block to execute if true coding CS Conditionals 7 animation using a conditional statement instead of modulo to a number in range CS105 03b Variables 8

5 conditional_dot (if) // conditional dot void draw() { background(255); println(mousex, mousex > width / 2); // the conditional statement if (mousex > width / 2) { fill(#ff0000); // red ellipse(0.75 * width, 50, 30, 30); line(width / 2, 0, width / 2, height); CS Conditionals 9 Nested Code Blocks CS Conditionals 10

6 see 04 Conditionals (trace) CS Conditionals 11 Rest Stop Analogy A single if statement is like deciding to stop at a rest stop on a highway CS Conditionals 12

7 conditional_dot (if else) // the conditional statement if (mousex > width / 2) { fill(#ff0000); // red ellipse(0.75 * width, 50, 30, 30); else { fill(#0000ff); // blue ellipse(0.25 * width, 50, 30, 30); CS Conditionals 13 Detour Analogy if else is like having to take a detour ( the if) or taking the original road (the else) CS Conditionals 14

8 What can this code draw? void draw() { background(200); A B if (mousey > 50) { fill(0); // black else { fill(255); // white ellipse(mousex, mousey, 20, 20); C D A, B, and C are all possible CS Conditionals 15 conditional_dot (if else if) // the conditional statement if (mousex > width / 2) { fill(#ff0000); // red ellipse(0.75 * width, 50, 30, 30); else if (mousex < width / 2) { fill(#0000ff); // blue ellipse(0.25 * width, 50, 30, 30); else { background(random(255)); CS Conditionals 16

9 Two Common Logic Errors with if statements Adding semicolon after the boolean expression means no code block. A code block with no "if" means always execute. // the conditional statement if (mousex > 50); { fill(#ff0000); // red ellipse(0.75 * width, 50, 30, 30); The if statement does nothing, and the code block will always draw the red ellipse. Fix this by removing the semicolon after the boolean expression. Missing "else" makes two if statements. // the conditional statement if (mousex > 50) { fill(#ff0000); // red ellipse(0.75 * width, 50, 30, 30); if (mousex < 50) { fill(#0000ff); // blue ellipse(0.25 * width, 50, 30, 30); else { background(random(255)); If mousex is greater than 50, the red ellipse is drawn. But then the second if statement tests if mousex is less than 50. It isn't, so the else code block is executed which covers the red ellipse with a random background. Fix this by added "else" before the second if statement. CS Conditionals 17 coding shaper checking what key was pressed if (key == 'c') { shape = 1; else if (key == 'r') { shape = 2; else if (key == 't') { using a variable to save 'state': if (shape == 1) { ellipse( ); else if (shape == 2) { rect( ); else if (shape == 3) { triangle( ); CS Conditionals 18

10 Equality vs. Assignment Operators == Equality Operator - is the left value equal to the right value? - e.g. state == 1 means "is state equal to 1?" - left and right can be anything that reduces to a single value (a variable, a function that returns a value, a number, an expression) = Assignment Operator - assign the right value to the left variable - e.g. state = 1 means assign 1 to state - left must be a variable, right can be anything that reduces to a single value (a variable, a function that returns a value, a number, an expression) CS Conditionals 19 Numerical Representation: Integers Binary Numbers: 1 and 0 Bits and Bytes Integer Representation: - Fixed size - How to Handle Negative Numbers? CS Conditionals 20

11 What is this binary number in decimal? 0101 A: 101 B: 8 C: 5 D: 4 E: 3 CS Conditionals 21 overflow // almost largest integer int a = ; void setup() { framerate(2); void draw() { a = a + 1; // watch the output! println(a); CS Conditionals 22

12 What does this code draw after 10 frames? int a = 0; void draw() { background(200); A B if (a < 5) { ellipse(50, 50, 50, 50); else { line(0, 0, 99, 99); a = a + 1; C D CS Conditionals 23 What does this code draw after 10 frames? int a = 0; void draw() { background(200); A B if (a < 5) { ellipse(50, 50, 50, 50); else if (a > 5) { line(0, 0, 99, 99); else { a = a + 1; C D CS Conditionals 24

13 Numerical Representation: Float A civil engineer doesn't care about the difference between 10 meters and meters meters is a huge difference for a microchip designer, but all measurements will be less than about 0.1 meters A physicist needs to use the speed of light (about ) and Newton's gravitational constant ( ) in the same equation CS Conditionals 25 Numerical Precision How many numbers are there between 0 and 1? How many decimal points in one-third (1/3)? Computers can not always do exact math println( * 0.01); println( * 0.01); This has implications for equality testing CS Conditionals 26

14 precision float a = 0; void setup() { framerate(2); void draw() { a = a + 1; if (a == 5) { background(255, 0, 0); // watch the console output! println(a); CS Conditionals 27 Guessing Game CS Conditionals 28

15 Boolean Expressions An expression that evaluates to true or false. boolean expressions with logical operators: - is your number greater than 50 and less than 60? - is your number less than 40 or greater than 80? - is your number not less than 32? CS Conditionals 29 Logical Operators is your number greater than 50 and less than 60? number > 50 && number < 60 is your number less than 40 or greater than 80? number < 40 number > 80 is your number not less than 32?! (number < 32) analogy CS Conditionals 30

16 Logical Operators && means "and" means "or"! means "not" CS Conditionals 31 Logical Operators CS Conditionals 32

17 Order of Operations first last CS Conditionals 33 Logical Operator Examples int a = 15; int b = 5; (a > 10 && b < 10) (a < b b < a) (a == 10 && a < 20 && b > 0) (a < > b * 2) (a + b > 16 b a > 0) (a > 10 && a < 12 b > 3 && b < 7)!(a > 10) coding CS Conditionals 34

18 logical_dot if (mousex > width / 2 && mousey < height / 2) { fill(#ff0000); // red ellipse(0.75 * width, 50, 30, 30); if (mousex > width / 2 mousey < height / 2) { fill(#ff0000); // red ellipse(0.75 * width, 50, 30, 30); CS Conditionals 35 (demo) extend shaper to work with CAPS LOCK on if (key == 'c' key == 'C') { shape = 1; CS Conditionals 36

19 What is drawn on the 6 th frame? int a = 0; int b = 0; A B void draw() { background(255); if (a < 10 b > 0) { ellipse(25, 25, 30, 30); else { rect(60, 60, 30, 30); a = a + 1; C D void mousepressed() { b = 100; CS Conditionals 37 What is drawn on the 50 th frame? int a = 0; int b = 0; A B void draw() { background(255); if (a < 10 b > 0) { ellipse(25, 25, 30, 30); else { rect(60, 60, 30, 30); a = a + 1; C D void mousepressed() { b = 100; CS Conditionals 38

20 What is drawn after the mouse is pressed? int a = 0; int b = 0; A B void draw() { background(255); if (a < 10 b > 0) { ellipse(25, 25, 30, 30); else { rect(60, 60, 30, 30); a = a + 1; C D void mousepressed() { b = 100; CS Conditionals 39 rect_hittest (roll over) // the hit test if (mousex >= x && mousex <= x + w && mousey >= y && mousey <= y + h) { fill(#ff0000); // red else { fill(255);... CS Conditionals 40

21 Boolean Variables The result of a relational expression is either true or false Boolean variables store true or false boolean a = 9 < 10; println(a); // prints true CS Conditionals 41 toggle boolean on = true; void draw() { if (on) { background(255); // white fill(255); else { background(30); // almost black fill(100); // navy ellipse(mousex, mousey, 30, 30); void mousepressed() { on =!on; CS Conditionals 42

22 mousepressed, mousepressed() mousepressed() is an event function - it's called once when the mouse button is pressed mousepressed is a built-in boolean variable - it's true when the mouse button is pressed, false otherwise Same for keypressed and keypressed() CS Conditionals 43 draw (extra demo) mousepressed pmousex pmousey keypressed keypressed() CS Conditionals 44

23 What is drawn on the 2 nd frame? boolean b = false; void draw() { background(200); A B if (b) { ellipse(50, 50, 50, 50); else { line(0, 0, 99, 99); b =!b; C D CS Conditionals 45