C# 5.0 Programmer's Reference

Exercises ❘ 229
Summary
In practice, it’s extremely difficult to anticipate every condition that might occur within a large
application. You should try to predict as many incorrect situations as possible, but you should also
plan for unforeseen errors. You should write error-checking code that makes bugs obvious when
they occur and recovers from them if possible. You may not anticipate every possible bug, but with
a little thought you can make the program detect and report obviously incorrect values.
You should also look for unplanned conditions (such as the user entering a phone number in a Social
Security number field) and make the program react gracefully. Your program cannot control everything
in its environment (such as the user’s actions, printer status, and network connectivity), but it
should be prepared to work when things aren’t exactly the way they should be.
You may never remove every last bug from a 100,000-line program, but you can make any remaining
bugs relatively harmless and appear so rarely that the users can do their jobs in relative safety.
Visual Studio provides a rich set of tools for debugging an application. Using the development environment,
you can stop the program at different lines of code and examine variables, change variable
values, look at the call stack, and call methods to exercise different pieces of the application. You can
step through the program, executing the code one statement at a time to see what it is doing. You can
even make some modifications to the source code and let the program continue running. Chapter 10,
“Tracing and Debugging,” describes tools and techniques you can use to debug applications.
Exercises
1. Consider the following Student class.
public class Student
{
public string Name;
public List Courses = new List();
}
// Constructor.
public Student(string name)
{
Name = name;
}
Add Debug.Assert statements to the class to require the following conditions.
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➤➤
The Name property must always be at least 1 character long.
The Courses value can never be null. (Although the list can be empty.)
2. Repeat Exercise 1 using code contract preconditions and postconditions instead of Debug
.Assert statements. (Put in postconditions even though you “know” they’re unnecessary.)
3. Repeat Exercise 1 using code contract invariants instead of preconditions, postconditions,
or Debug.Assert statements.
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