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Chapter 4: Problem 15

Why should you be careful when choosing a sentinel value?

Short Answer

Expert verified
Provide an example.

Step by step solution

01

Understand the concept of sentinel values

A sentinel value is a special value used in programming to indicate the end of a data sequence or as a marker during looping or input processing. In most cases, sentinel values are used in conditions to control loops, such as in while loops, to know when to stop looping or when there are no more values to process.
02

Know the importance of choosing an appropriate sentinel value

It is essential to choose an appropriate sentinel value that does not appear in the regular data sequence. An inappropriate sentinel value could cause the loop to terminate prematurely or lead to unwanted results. If the sentinel value appears in the regular data sequence, it may be mistaken as the end of the sequence, causing the loop to stop and not process all the required data.
03

Example of choosing an inappropriate sentinel value

Let's assume we have an input stream of integers, and we need to find the sum of these integers. Our sentinel value is -1, which means the loop will stop when it encounters -1. The input sequence is: 3, 2, 5, -1, 4, 6 In this case, we will stop processing the input when we encounter the sentinel value (-1). However, this means that the last two integers (4 and 6) will not be considered in the sum, leading to an incorrect result.
04

Importance of choosing the right sentinel value

To avoid such issues, make sure to choose a sentinel value that will not appear in the regular data sequence or use a different method to control the loop. In the example above, we could have used an input delimiter (e.g. end of a line, or a different non-numeric character) or taken the number of inputs expected prior to entering the loop to ensure correct processing. When working with real-world applications, carefully consider the data you expect to process and choose a sentinel value that will not interfere with the correct operation of the program.

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