Announcements

1. Announcements • Section Voting is up • Vote in your section by Thursday, 10pm • Assignment: 20 pts for voting • Two labs this week: • Web App Design Lab • Coin Flipping Lab • You decide the order that you do them Katherine Deibel, Fluency in Information Technology

2. INFO100 and CSE100 Fluency with Information Technology Arrays & IterationGoing beyond one Katherine Deibel Katherine Deibel, Fluency in Information Technology

3. Learning Programming • Programmer Braggery:How many languages do you know? • The answer really does not matter • Many languages are regional dialects of each other (share syntax and concepts) • Javascript, Java, C#, and Visual Basic are all object-oriented languages • Scottish accent, Southeast U.S. accent, Boston accent, London accent Katherine Deibel, Fluency in Information Technology

4. When faced with a new language… • I look for how to do the following: • Declare variables • If-Else statements • Make and use functions • Manipulate strings • Loops and iteration • Arrays  Labs 7 & 8 and Project 2  Today's lecture The Takeaway:You have learned the basics for working in many different programming languages. Katherine Deibel, Fluency in Information Technology

5. Definitions • Iteration, or looping, is the process of repetition: • looping through a sequence of statements to repeat them Katherine Deibel, Fluency in Information Technology

6. Major Types of Repetitions • For loop • Run a fixed number of times • While loop • Run 0+ times until condition is met • Do while loop • Run 1+ times until condition is met Katherine Deibel, Fluency in Information Technology

7. For Loops Do I need to repeat myself? Katherine Deibel, Fluency in Information Technology

8. For Loop Basic Syntax for (<initial>; <condition>; <next>){ <statement list>} • Program completes the entire statement sequence of the <statement list> during each iteration Katherine Deibel, Fluency in Information Technology

9. Control Specification • The three operations in the parentheses of the for loop • Control the number of times the loop iterates • by using an iteration variable (must be declared) Katherine Deibel, Fluency in Information Technology

10. How a For Loop Works • Consider a computation on declared variables j and text • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) • { • text = text + "Never! "; • } • alert(text); Katherine Deibel, Fluency in Information Technology

11. How a For Loop Works • Consider a computation on declared variables j and text • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) • { • text = text + "Never! "; • } • alert(text); control specification Katherine Deibel, Fluency in Information Technology

12. How a For Loop Works • Consider a computation on declared variables j and text • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) • { • text = text + "Never! "; • } • alert(text); initialization Katherine Deibel, Fluency in Information Technology

13. How a For Loop Works • Consider a computation on declared variables j and text • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) • { • text = text + "Never! "; • } • alert(text); continuation condition Katherine Deibel, Fluency in Information Technology

14. How a For Loop Works • Consider a computation on declared variables j and text • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) • { • text = text + "Never! "; • } • alert(text); step size or increment Katherine Deibel, Fluency in Information Technology

15. How a For Loop Works • Consider a computation on declared variables j and text • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) • { • text = text + "Never! "; • } • alert(text); NO SEMICOLONS!! Katherine Deibel, Fluency in Information Technology

16. Processing for Loops • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) { • text = text + "Never! "; • } • alert(text); Step One: <initialization> • Sets (and maybe declares) the iteration variable's value for the first iteration of the loop • Initialization is done only once • Example: j is declared and set to 1 Katherine Deibel, Fluency in Information Technology

17. Processing for Loops • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) { • text = text + "Never! "; • } • alert(text); Step Two: <continuation> • The <continuation condition> is tested • If true, the statement list is computed. • If false, the <statement list> is skipped and control passes to the statement after the for loop • Example: j <= 3 and text = … Katherine Deibel, Fluency in Information Technology

18. Processing for Loops • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) { • text = text + "Never! "; • } • alert(text); Step Three: <next iteration> • The <next iteration> statement is computed • Loop returns to Step Two • Example: j = j + 1 Katherine Deibel, Fluency in Information Technology

19. Example • text = "She said "; • for ( var j = 1; j <= 3; j = j + 1 ) { • text = text + "Never! "; • } • alert(text); Katherine Deibel, Fluency in Information Technology

20. A World-Famous Iteration • for ( vari= 0; i< n; i++ ) {…} • Most frequently written for loop • Easy to see iteration count: • Always runs n times • Goes from 0 to n-1 Katherine Deibel, Fluency in Information Technology

21. For Loop Syntax: Initialization • The Iteration Variable • Must be declared in the loop or in the code before the loop • Must follow rules for variable identifiers • i, j, and k are the most common choices • The Starting Point • Iteration can begin anywhere, including negative numbers Katherine Deibel, Fluency in Information Technology

22. For Loop Syntax: Continuation • Continuation/Termination Test • Test is any expression resulting in a Boolean value (true/false) • Continuation must involve iteration variable to avoid infinite loop Katherine Deibel, Fluency in Information Technology

23. For Loop Syntax: Step Size • The amount of change in the iteration variable from one iteration to the next • Often called the increment or decrement • Increment: j = j + 1 • Decrement: j = j – 1 • Often uses shorthand: j++ or j-- • Can be any size • j = j + 5 • j -= 2 Katherine Deibel, Fluency in Information Technology

24. Nested for Loop Syntax for (<initial i>; <condition i>; <next i>) { <some statements> for (<initial j>; <condition j>; <next j>) { <some statements> } <some statements> } Katherine Deibel, Fluency in Information Technology

25. Three-Level Nested For Loop • for( vari= 1; i<= N_i; i++ ) • { • for( var j= 1; j<= N_j; j++ ) • { • for( vark = 1; k <= N_k; k++ ) • { • } • } • } Katherine Deibel, Fluency in Information Technology

26. Syntax vs Logic Errors • There are two ways to go wrong when programming • Syntax Errors  how the code is written • Logic Errors  what the code does • Remember: Just writing code that runs does not mean it runs correctly for (var j = 5; j > 0; j++) ;{ //statement body} • Syntactically correct code • Runs forever (BAD!) Katherine Deibel, Fluency in Information Technology

27. Complex Loop Conditions • Loop conditions can be fairly complex • The above loop will run 8 times unless total becomes zero or negative first • for (var j = 0; j < 8 && total > 0; j++){ //statement body} Katherine Deibel, Fluency in Information Technology

28. Arrays and Indexes Storing a Collection of Items Katherine Deibel, Fluency in Information Technology

29. What is an Array? • An indexed list of items • Indexed means each element in the list has a number, or index Katherine Deibel, Fluency in Information Technology

30. What is an Array? • George Washington • John Adams • Thomas Jefferson • James Madison • James Monroe • John Quincy Adams • Andrew Jackson • Martin Van Buren • William Harrison • John Tyler • James Polk • Zachary Taylor • Millard Fillmore • Franklin Pierce • James Buchanan • Abraham Lincoln • Andrew Johnson • Ulysses S. Grant • Rutherford B Hayes • James Garfield • Chester Arthur • Grover Cleveland • Benjamin Harrison • Grover Cleveland • William McKinley • Theodore Roosevelt • William H. Taft • Woodrow Wilson • Warren Harding • Calvin Coolidge • Herbert Hoover • Franklin D. Roosevelt • Harry S. Truman • Dwight Eisenhower • John Kennedy • Lyndon Johnson • Richard Nixon • Gerald Ford • James Carter • Ronald Reagan • George H. W. Bush • William Clinton • George W. Bush • Barack Obama Katherine Deibel, Fluency in Information Technology

31. Indexing • Process of creating a sequence of names by associating a base name with a number (like Apollo 13 or Henry VIII) • Each indexed item is called an element of the base-named sequence Katherine Deibel, Fluency in Information Technology

32. Indexing and Iteration • Index Syntax • Index number is enclosed in square brackets [ ] • Iterations can be used to refer to all elements of a name • A[j] for successive iterations over j referring to different elements of A Katherine Deibel, Fluency in Information Technology

33. Where is the first element? • Index Origin • The point at which indexing begins (the least index) • First element • In life, the first element may begin with 1, or have no number (Queen Elizabeth) • JavaScript and most programming languages always uses index origin 0 Katherine Deibel, Fluency in Information Technology

34. JS Syntax for Arrays • with name and # elementsvar books = new Array(6); • with name and elementsvar shapes = new Array("square","circle","triangle"); Katherine Deibel, Fluency in Information Technology

35. JS Syntax for Arrays (cont.) • Accessing elements in array shapes[1] is "circle" • Changing element in array shapes[0] = "rectangle"; • Adding more elements to the array shapes[3] = "ellipse"; shapes[4] = "heptagon"orshapes.push("diamond"); adds to the end of the array Katherine Deibel, Fluency in Information Technology

36. Referring to an Array Element • Referencing an element of the array:shapes[<index>] • Index must be a non-negative integer or expression or variable that resolves to non-negative integer shapes[1] = …i=3; shapes[i] = … shapes[i+2] = … Katherine Deibel, Fluency in Information Technology

37. Iteration and Arrays • array.length returns the highest index in the array (the number of elements in it) • for( vari=0; i<shapes.length; i++) • { • } Katherine Deibel, Fluency in Information Technology

38. Iteration and Arrays vari, text=""; /*declare iteration and other variables*/ var fruits = new Array( 'lemons','apples','mangoes','tangerines','kumquats', 'cantaloupe','peaches','grapefruit','raspberries'); alert("Total number of fruits is " + fruits.length); for (i=0; i<fruits.length; i++) { text += i + '. ' + fruits[i] + '<br/>'; } document.write("<h1>Elements of Fruits Array:</h1><p>" + text + "</p>"); Katherine Deibel, Fluency in Information Technology

39. While & Do While Loops More looping… <nausea> Katherine Deibel, Fluency in Information Technology

40. Uncertain number of repeats • For loops are good when a fixed number of repetitions is needed • The number of repetitions may not be known a priori • Example: Weight limits on an elevator • Get weight of next person in line • If weight plus total so far is less than limit, that person gets on • Once limit is passed, last person gets off and elevator goes up Katherine Deibel, Fluency in Information Technology

41. Example While Loop • /* weights is an array of people's weights • limit is the elevator's weight limit */ • varcurrWeight = 0; • varj = 0; • while (weights[j] + currWeight <= limit) • { • currWeight = currWeight + weights[j]; • j = j + 1; • } Katherine Deibel, Fluency in Information Technology

42. Do While Loops • In the previous example, the loop would not run if the first person exceeded the weight limit • While loops can run zero or more times • Do while loops always run at least once • do { • <statements> • } while (condition); Katherine Deibel, Fluency in Information Technology

43. A note about semicolons • Semicolons do NOT go after the loop statement for for loops and while loops • for( vari=0; i<n; i++) • { • } • while(x<=maximum) • { • } • There IS a semicolon after the loop statement for a do while loop. • do { • <statements> • } while (condition); Katherine Deibel, Fluency in Information Technology

44. Summary • Loops allow us to repeat steps • Arrays are a means for working with multiple values • These are the last of the essential aspects to programming Katherine Deibel, Fluency in Information Technology