ITEC 120 2008spring ibarland, jdymacek

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lect01c-friPizzaArea-comparisons
comparing three approaches

We consider several different possible solutions to writing friPizzaArea. They all give the same answers, but some are better than others.

We see from our test cases, that the answer we want is the same as pizzaArea, with an extra 113 square inches. That naturally suggests:

double friPizzaArea_v1( double diam ) {
  return 3.14*(diam/2)*(diam/2)+113.04;
  }

Here is a barely-different version -- only some added spaces and parentheses -- yet it is decidably a bit better:

double friPizzaArea_v2( double diam ) {
  return (3.14*(diam/2)*(diam/2)) + 113.04;
  }

A related way of writing this would be:

double friPizzaArea_v3( double diam ) {
  return (3.14*(diam/2)*(diam/2))
       + (3.14*(12.0/2)*(12.0/2));
  }

• Version 2 is shorter.
• Version 3 makes it clear why the number 113.04 is used. Imagine if the offer were changed to only give away a 10″ pizza. The second would be easy to update; the first would take more effort.
• If there is an error/typo, it would be easier to spot in version 3.
• If somebody else were looking at the code (to modify it, or searching for the cause of a bug, or whatever), version 3 is a little clearer about what the code means to be computing.

Here is yet another variant:

double friPizzaArea_v4( double diam ) {
  return 0.785*(diam*diam + 144);
  }

This last version is the most different:

double friPizzaArea_v5( double diam ) {
  return pizzaArea(diam) + pizzaArea(12);
  }

• Version 5 makes it precisely clear what the code is computing.
• Version 5 is also clearly exactly correct (given that we've already tested pizzaArea).
• Suppose that Krusteaz Pizza Korporation, in its never-ending quest to be different from the competition, decides to start making all their pizzas triangular. How would our code have to change?
  Clearly, we'd have to re-write pizzaArea to have the area of a triangle, rather than a circle. If we'd used any of Versions 1-4, we'd also have to remember that those versions also depend on the exact shape of a pizza. But, Version 5 would not need any further update -- it is “robust”.

Introducting this

Alas, there is one problem Version 5. Do you remember, how we call a function, in Java? Our mantra:

To call a function: object   dot   functionName   openParen   argument

double friPizzaArea_v6( double diam ) {
  return this.pizzaArea(diam) + this.pizzaArea(12);
  }

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©2008, Ian Barland, Radford University Last modified 2008.Jan.24 (Thu)

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