Chapter 3 - Selections

Class 1:

Moodle Chapter 2 Quiz (5 min)
3.1-3.5 Boolean type, if statements, if-else statements (40:34)
On your own after class 1 and before class 2: 3.6 Common pitfalls (44:17)

Class 2:

3.7, 9.6.2 Pseudorandom number generation (26:37)
3.10 Logical operators (21:38)
As remaining class time permits: In-class exercise (below)

Class 3:

3.13 Switch statement (8:07)
3.14 Conditional expression (a.k.a. selection operator, ternary operator, if-else expression) (9:42)
3.15 Operator precedence and associativity (7:48)
3.16 Debugging basics in Eclipse (9:48)
As remaining class time permits: In-class exercise (below)

In-class exercise: Rock-Paper-Scissors

(text exercise 3.17 modified) Call your program RockPaperScissors.java.
Input: an integer 0, 1, or 2, representing a play of "rock", "paper", or "scissors", respectively.
Output:

Before the input: a prompt "Please enter 0 (rock), 1 (paper), or 2 (scissors): "
After the input:

The computer randomly chooses an integer to represent it's play.
Print "I played <play>." where <play> is "rock"/"paper"/"scissors" depending on the computer's randomly chosen integer.
Print "You win."/"You lose."/"Draw." based on the following rules:

Rock wins against scissors.
Scissors wins against paper.
Paper wins against rock.
Players that choose the same play draw (i.e. tie).

Hint: At no point should you have an if-else chain for 9 cases. Each of the last two print statements should require at most 3 cases each. Let the user's play be p1 and the computer's play be p2. Consider what value you get if you compute (p1 - p2 + 3) % 3. How does the result of this computation map to the win/lose/draw cases? Why does this work? Why wouldn't the expression (p1 - p2) % 3 suffice for our three cases?

Example transcripts (input underlined):

Please enter 0 (rock), 1 (paper), or 2 (scissors): 0
I played paper.
You lose.

Please enter 0 (rock), 1 (paper), or 2 (scissors): 1
I played rock.
You win.

Please enter 0 (rock), 1 (paper), or 2 (scissors): 2
I played scissors.
Draw.