CS141: Topics for Week 7: Oct 9, 11, 13, 2017

Computer Science Headlines: ACM Tech News

Mon: Continue from Last Week

• Go over exam 1
• Finish discussion of GUIs

Reading:

• Chap 6: Loops

Lab and Other Activities

• Lab 6: Loops and Cards
• In Class Practice Activities
  • Use a loop to print out the lyrics for 99 Bottles of Beer on the Wall.
  • How does one represent a card?
  • What is the UML Diagram for the BlackJack Game?
  • Do all of these!! Basic Looping Problems (pdf)
  • Once we get to nested loops, do all of these!! Nested Loop Problems (pdf)
  • By the end of the chapter, you should be able to do all of these practice problems without blinking an eye! They are the kind of coding questions you might see on an exam.
  • BlackJack Preliminaries:
    • Write a loop that prompts a user for a yes or no. If they don't answer correctly, then keep prompting them until they do.
    • Write code to randomly pick a card (index 0-51) and calculate & print the suit (index 0-4) and face (index 0 to 12).
    • Write a loop that draws 10 random playing cards, each time printing the name of the card. Note, to print the name, one can use unicode

           if (suit == 0) {  // spades
               name = "\u2660";
           } else if ...
      

      Look up online the unicode for the other suits.
    • Add code to compute the value of the card (2-10 for face cards, 10 for JKQ, 1 or 11 for Ace)

Lecture Discussion Topics:

• Why do we have loop structures?
  Repetition - print the numbers from 1 to 5. What about 10 to 1000?
  Repetition more generally - print the numbers starting at n1 and ending at n2.
• Components of any loop:
  • Loop variable - the variable that controls the looping
  • Loop variable initialization - the starting value of the loop variable.
  • Loop condition - this must be true for loop to continue
  • Loop variable update - how does loop variable change after each loop
  • Loop body - sequence of statements that are executed in the loop
• Types of loops:
  • while-loops - used when the number of repetitions can't be predicted ahead of time (indefinite)
  • for-loops - when you know precisely how many times you will loop (definite). Loop variable only defined within loop.
  • do-while-loops - checks condition at end; always executes the body at least once
• Figuring out what is going on - Hand tracing, unraveling the loop
• Common Errors: infinite loops, off-by-one
• Sentinel values - the user controls when to stop
• Checking for correct user input and break statements
• Common applications: Basic Looping Problems (pdf)
• Book examples: computing sums, averages, all matches, first match, max values, min values, comparing adjacent values
• Nested loops. See Nested Loop Problems (pdf)
• Random numbers and games- rolling a die, picking a card.
• Monte Carlo method

Concepts and Vocabulary