Homework 2

CS17

40 pts.

1. Design pseudocode to control a soda machine. (As an aside, why wouldn't we refer to this pseudocode as an algorithm?) The machine stocks 4 kinds of soda: Coke (50 cents), Diet Coke (50 cents), root beer (65 cents --- it's really good stuff), and Mountain Dew (40 cents, the favorite of hackers).

   Inputs:

   • Coins: nickels, dimes, quarters
   • Button pushes, corresponding to the 4 kinds of soda
   • Indications from the four soda compartments as to whether or not each one is empty

   Outputs:

   • A soda (possibly)
   • Change (possibly)

   I want you to do the requirements specification, analysis, and design steps for this problem. Your design is the most important part. Your pseudocode design should demonstrate top-down stepwise refinement.

Requirements Specification

Wait in a continuous loop, monitoring the machine:

• Coin drops
• Soda available
• Button pushes

Analysis

Inputs:

• Coins: nickels, dimes, quarters
• Button pushes, corresponding to the 4 kinds of soda
• Indications from the four soda compartments as to whether or not each one is empty

Outputs:

• A soda (possibly)
• Change (possibly)

Conditions:

• Coke and Diet Coke are 50 cents, Mountain Dew is 40 cents, and root beer is 65 cents.
• If change equal to at least the amount of the soda desired has been entered, a soda will be dropped (if one is available), and any change returned.
• If a soda is not available, or insufficient change has been put into the machine, the change is returned.

Top-Down Stepwise Refinement

Design

let deposit = 0
while forever
   if quarter dropped
      let deposit = deposit + 25
   else if dime dropped
      let deposit = deposit + 10
   else if nickel dropped
      let deposit = deposit + 5
   else if mountain dew selected
      if deposit >= 40 and mountain dew is available
         drop mountain dew
         let deposit = deposit - 40
      end_if
      return remaining deposit
      let deposit = 0
   else if coke selected
      if deposit >= 50 and coke is available
         drop coke
         let deposit = deposit - 50
      end_if
      return remaining deposit
      let deposit = 0
   else if diet coke selected
      if deposit >= 50 and diet coke is available
         drop diet coke
         let deposit = deposit - 50
      end_if
      return remaining deposit
      let deposit = 0
   else if root beer selected
      if deposit >= 65 and root beer is available
         drop root beer
         let deposit = deposit - 65
      end_if
      return remaining deposit
      let deposit = 0
   end_if
end_while