Exceptions and pre-conditions
An exception is an anomalous or exceptional condition requiring special processing – often changing the normal flow of program execution[2].
Be careful not to confuse an exception with an error.
An error "indicates serious problems that a reasonable application should not try to catch." An Exception "indicates conditions that a reasonable application might want to catch."[3].
We use the term "catch an exception" to catch exceptions and plan how the program should respond.
Identifying exceptions[edit]
The exceptions below are common. There are many other types of exceptions.
- consider different data types (are you passing an int to a function which is expecting a string?)
- consider inaccurate user input (accidental or deliberate)
- consider writing or reading a to file - there could be a failure opening, writing, or closing to file
- consider memory limitations - this is especially important when you are working with large datasets
- consider the possibility a user might attempt to interrupt the program (usually by pressing control-C).
For a list of common exceptions, please click here
Example[edit]
I am writing a program to calculate your final grade. The program accepts as input your name, all your grades, averages them, and then outputs your name and a final score.
What exceptions might we consider?
- What if a student is missing a score?
- What if a score is non-standard (instead of an integer, we have a letter)?
- What if a there is non-standard character in a student name?
Standards[edit]
These standards are used from the IB Computer Science Subject Guide[4]
- Identify exceptions that need to be considered in a specified problem solution.
References[edit]
- ↑ http://www.flaticon.com/
- ↑ https://en.wikipedia.org/wiki/Exception_handling
- ↑ https://stackoverflow.com/questions/5813614/what-is-difference-between-errors-and-exceptions
- ↑ IB Diploma Programme Computer science guide (first examinations 2014). Cardiff, Wales, United Kingdom: International Baccalaureate Organization. January 2012.