Exception Handling: Processing an Out-of-Range Subscript

An exception indicates a problem that occurs while a program executes. The name “exception” suggests that the problem occurs infrequently—if the “rule” is that a statement normally executes correctly, then the problem represents the “exception to the rule.” Exception handling enables you to create fault-tolerant programs that can resolve (or handle) exceptions. In many cases, this allows a program to continue executing as if no problems were encountered. For example, Fig. 7.25 still runs to completion, even though an attempt was made to access an out-of-range subscript. More severe problems might prevent a program from continuing normal execution, instead requiring the program to notify the user of the problem, then terminate. When a function detects a problem, such as an invalid array subscript or an invalid argument, it throws an exception—that is, an exception occurs. Here we introduce exception handling briefly. We’ll discuss it in detail in Chapter 17, Exception Handling: A Deeper Look.