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Design and Implementation*

Design and Implementation*. Objective: To design and implement a program for a relatively small yet reasonably complicated problem. To introduce and review a variety of implementation languages and to have students review the pros and cons of different implementation choices and languages.

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Design and Implementation*

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  1. Design and Implementation* • Objective: To design and implement a program for a relatively small yet reasonably complicated problem. To introduce and review a variety of implementation languages and to have students review the pros and cons of different implementation choices and languages. • “Show me your flowcharts and conceal your tables, and I shall continue to be mystified. Show me your tables, and I won’t usually need your flowcharts; they’ll be obvious” – Frederick P. Brooks, The Mythical Man Month *The examples in these slides come from Brian W. Kernighan and Rob Pike, “The Practice of Programming”, Addison-Wesley, 1999.

  2. Themes • “Once the data structures are laid out, the algorithms tend to fall into place, and the coding is comparatively easy” • The choice of programming language is relatively unimportant to the overall design. • Comparing implementations demonstrates how languages can help or hinder, and ways in which they are unimportant.

  3. Topics • Problem: Generate random English text that reads well. • Program: some data comes in, some data goes out, and the processing depends on a little ingenuity. • Implementations: C, C++, Java, Perl

  4. Failed Attempts • Generate random letters (even with proper frequency. • Generate random words chosen from a dictionary • Need a statistical model with more structure (frequency of whole phrases)

  5. Markov Algorithm • set w1 and w2 to the first two words in the text • print w1 and w2 • loop: • randomly choose w3, one of the successors of w1 and w2 (in sample text) • print w3 • replace w1 and w2 by w2 and w3

  6. Sample Markov Algorithm • Input Prefix: • show your • your flowcharts • flowcharts and • flowcharts will • your tables • will be • be mystified • be obvious • Suffix words that follow • flowcharts tables • and will • conceal • be • and and • mystified. obvious. • Show • (end)

  7. Hash Table to Find Suffix Following Two Word Prefix a state: “show” pref[0] pref[1] “your” “flowcharts” suf a suffix: next word next another state: another suffix: pref[0] pref[1] word “tables” suf next next

  8. Implementation • See lecture outline for links to 4 different implementations • C (see Makefile) • C++ • Java • Perl • What are the pros and cons of the different implementations?

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