Question

Mark the following statements as true or false. a. In a counter-controlled while loop, it is not necessary to initialize the loop control variable. b. It is possible that the body of a while loop may not execute at all. c. In an infinite while loop, the while expression (the decision maker) is initially false, but after the first iteration it is always true. d. The while loop: \(j=0\) while \((\mathrm{j}<10)\) \(\mathrm{j}++;\) terminates if \(j>10\) e. A sentinel-controlled while loop is an event-controlled while loop whose termination depends on a special value. f. \(\quad\) A loop is a control structure that causes certain statements to execute over and over. g. To read data from a file of an unspecified length, an EOF-controlled loop is a good choice. h. When a while loop terminates, the control first goes back to the statement just before the while statement, and then the control goes to the statement immediately following the while loop.

Short answer

a. False, b. True, c. False, d. False, e. True, f. True, g. True, h. False.

Step-by-step solution

Evaluate Statement a

The statement says that in a counter-controlled while loop, initializing the loop control variable is not necessary. This is false because initializing the loop control variable is essential to set it to a known value before starting the loop to ensure the loop executes correctly.

Evaluate Statement b

The statement claims that it's possible for a while loop's body not to execute at all. This is true because if the while loop's condition is false at the start, the loop's body will not execute even once.

Evaluate Statement c

The statement suggests that the while expression in an infinite loop is initially false and becomes true after one iteration. This is false because in an infinite loop, the condition remains true from the beginning, causing the loop to run indefinitely.

Evaluate Statement d

The loop shown increments `j` each time until `j < 10` is false. The statement says it terminates if `j > 10`, which is false because the loop condition checks `j < 10`, and thus it stops once `j` equals 10.

Evaluate Statement e

The statement describes a sentinel-controlled while loop that terminates based on a special value. This statement is true as a sentinel value, when encountered, ends the loop.

Evaluate Statement f

The statement says a loop is a control structure that executes certain statements repeatedly. This is true because loops are specifically meant to execute a block of code multiple times until a specified condition is met.

Evaluate Statement g

The statement claims that using an EOF-controlled loop is suitable for reading a file of an unspecified length. This is true because EOF-controlled loops continue to read data until the End Of File marker is reached.

Evaluate Statement h

The statement suggests control first returns to the statement before the while when it terminates. This is false; once a while loop terminates, control moves directly to the statement after the loop.

Key concepts

counter-controlled loop

In programming, a counter-controlled loop, as the name suggests, revolves around the concept of counting. This type of loop has three main components:

• Initialization
• Condition
• Increment or decrement

Initialization is crucial, as it sets up the loop control variable to a known starting value. After initialization, the loop checks a condition to determine whether the loop should execute. If true, the loop body executes, followed by an increment or decrement of the counter.
For example, a simple counter-controlled loop might look like this: ```plaintext j = 0 while (j < 5) { // loop body j++; } ``` In the snippet above, `j` starts at 0, and the loop runs until `j` equals 5. This ensures that the loop executes exactly 5 times. Proper initialization and control are critical to prevent logic errors or infinite loops, which can occur if the counter is not handled correctly.

sentinel-controlled loop

A sentinel-controlled loop differs from a counter-controlled loop because its termination relies on a special value known as a "sentinel." This value signifies to the loop that it should stop executing.
Sentinel-controlled loops are particularly useful when dealing with input that does not have a predetermined count, like reading a list of numbers until a special number, say -1, is encountered:

• There is no need to know the number of iterations in advance.
• It allows dynamic termination when processing data sequences.

Imagine collecting exam scores from users inputting numbers until they enter `-1`. The loop continues until the sentinel value `-1` is input, signaling to stop reading scores and perhaps calculate an average. This mechanism offers flexibility because the loop continues to process data until the specific sentinel value is detected, making it handy for varying data lengths.

EOF-controlled loop

An EOF-controlled loop is typically used for reading data from files where the length is not predetermined. "EOF" stands for "End Of File," and this type of loop continues until the end of the file is reached. It is designed to process data streams where the exact count of data is unknown until the file has been fully read.
Consider reading an entire file line by line until no more lines are available: ```plaintext while (Reader.readLine() != null) { // Process line } ```

• The loop checks if there is another line to read.
• It runs until `readLine()` returns `null`, indicating the end of the file.

EOF-controlled loops are particularly efficient in file handling tasks, ensuring that processing continues seamlessly until all data is consumed, encapsulating the entire reading operation in a single, cohesive loop structure.

infinite loop

An infinite loop is a loop that does not have an end condition that can eventually become false, thus runs endlessly unless externally interrupted. While often not intentional, infinite loops can be useful in certain situations such as servers waiting to receive new input.
The irony of an infinite loop is its very useful need for caution. Consider the following simplistic infinite loop example: ```plaintext while (true) { // continuously execute } ```

• Always evaluates to true.
• Never has a natural stopping point.

These loops can be beneficial for applications that need to run continuously without interruption, such as games or services monitoring events. However, it is critical to handle these loops responsibly. If a break condition is ignored, they can lead to unresponsive software, resource exhaustion, or even crashes. Therefore, infinite loops are best managed with well-defined emergency exit conditions or manual termination to maintain control over application flow.