Question

What type of loop, such as counter-control and sentinel-control, will you use in each of the following situations? a. Sum the following series: \(1+(2 / 1)+(3 / 2)+(4 / 3)+(5 / 4)\) \(+\ldots+(10 / 9)\) b. Sum the following numbers, except the last number: 17,32,62,48,58,-1 c. A file contains an employee's salary. Update the employee's salary.

Short answer

a. Counter-control loop, b. Sentinel-control loop, c. File processing loop.

Step-by-step solution

Identify the Type of Series or List

For part (a), we have a finite series from 1 to 10 with a clear endpoint. This implies using a counter-controlled loop is appropriate as we know the exact number of iterations needed.

Determine Loop for Unknown Length Data

In part (b), we need to sum numbers until a sentinel value (-1) is encountered, which suggests using a sentinel-controlled loop. This loop will continue summing values until it reads -1, which serves as the stopping condition.

Consider Loop for File Processing

Part (c) involves reading and updating data from a file, likely requiring iteration over data entries. A file processing loop or a generic loop (like a while or for-each) would be used to traverse through each salary record, update it, and then move to the next.

Key concepts

Counter-Controlled Loop

In programming, a counter-controlled loop runs for a specific number of iterations, which means you know exactly how many times the loop will execute before it begins. It's perfect for tasks where the number of iterations is predetermined.
For example, in calculating the sum of a series like:

• 1 + \( \frac{2}{1} \) + \( \frac{3}{2} \) + \ldots + \( \frac{10}{9} \)

you know in advance that the loop will iterate exactly ten times. Such loops often use a counter variable that is incremented or decremented to track how many times the loop has executed. You can think of this loop as a way of counting from a start to an end point. Here's a simple way to understand it:
The counter starts at the first term, and with each iteration, the counter increases to represent the next term. This continues until you reach the last term. This predictability makes counter-controlled loops efficient for processing sequences where the length is known beforehand.

Sentinel-Controlled Loop

A sentinel-controlled loop is useful for scenarios where you don't know how many times the loop needs to run. Instead, the loop continues until a special value, known as the sentinel, is encountered.

• Imagine you have a list of numbers that you need to add up, such as 17, 32, 62, 48, 58 and the task is to stop once you hit -1.

The -1 here acts as a sentinel value, indicating the stopping point. The loop checks each number, adds it if it's not the sentinel, and stops the process once the sentinel is reached. This method is ideal for processing data in real-time or from inputs where the endpoint isn't known at the start.
In implementation, you continuously process input until you see the sentinel. It's dynamic and flexible, making it widely used in file reading, user input processing, and more, where the data length isn't predetermined.

File Processing

When working with files, loops are your tool for efficiently traversing through the data within those files. File processing requires certain strategies, especially if you need to read, process, and update data such as employee salaries one entry at a time.
The loop here can be a simple structured loop that reads each line (or entry) of the file, modifies the salary as instructed, and then moves on to the next entry. This could be a while loop or for-each loop depending on the file handling mechanism of your programming language.

• Read the file line by line
• Extract necessary data
• Perform operations such as updating the salary
• Write back the updated data if necessary

File processing loops make it possible to handle each entry effectively. They offer a way to handle large data sets by processing in manageable portions. Every entry can be treated independently or cross-referenced with previous reads depending on the task at hand.