Topdown design

1
(No Transcript)
2
Top-down design

• Outline the project in the boldest steps
  possible, do not worry about how to achieve each
  step
• It is to be expected that some steps are beyond
  your immediate understanding
• Consider each step, refine it as much as
  possible, go to another step if you run into
  trouble
• If you are dealing with a computer program,
  continue to refine until the steps are program
  language commands

3
Example 1 opening a restaurant

• Choose a Theme
• Pick a neighborhood
• Find a Site
• Compute the Costs
• Acquire the Funds
• Build it
• Get the Staff
• Prepare the Ads

• Compute the Costs
• - Hire an architect, get the building costs
• - Determine costs of utilities, trash removal,
  etc.
• - Evaluate Labor Costs
• - Evaluate Publicity Costs

4
Example 2 merging files

• Consider a large file of names and phone numbers
• a telephone directory for a large city
• Consider a smaller file of new names and phone
  number which must be added to the original list
• new phone numbers added today
• Design a procedure (a program?) that will merge
  these two files into a new phone directory

5
Example 2 merging files

• 1. Alphabetize OLDLIST
• 2. Alphabetize ADDLIST
• 3. Create a blank file, call it NEWLIST
• 4. Merge OLDLIST and ADDLIST into NEWLIST
• 5. Delete OLDLIST
• 6. Delete ADDLIST
• 7. Rename NEWLIST, calling it OLDLIST

6
Example 2 merging files

• 1. Alphabetize OLDLIST
• (already done, it was yesterdays output.)
• 2. Alphabetize ADDLIST
• (learn how to sort stuff, too much trouble to
  describe here.)
• 3. Create a blank file NEWLIST
• (easy to do)

7
Example 2 merging files

• 4. Merge OLDLIST and ADDLIST into NEWLIST
• A. read the first item of OLDLIST, call it OLD,
  read the first item of ADDLIST, call it ADD
• B. compare OLD with ADD, write the smaller of
  them to NEWLIST, read the next item to replace
  it.
• C. if you have not run out of file OLDLIST or
  ADDLIST, return to B again, otherwise go to D.
• D. If you have drained ADDLIST, read the rest of
  OLDLIST into NEWLIST, if you have drained
  OLDLIST, read the rest of ADDLIST into NEWLIST.

8
Example 2 merging files

• 5. Delete OLDLIST
• 6. Delete ADDLIST
• 7. Rename NEWLIST, calling it OLDLIST

9
Two parts of a function definition

• int Cube ( int n )
• return n n n
• The heading declares the functions name,
  specifying its return type and the name and type
  of each of its parameters
• The body is a compound statement (block) which
  defines the behavior of the function

Heading
Body