Question

Rewrite the following program segment using a repeat structure rather than a while structure. Be sure the new version prints the same values as the original. Initialization: num \(=0\) while \((\) num \(<50)\) : if (num is Odd) : print (num is Odd) \(=\) num \(+1\) num \(=\) num \(+1\)

Short answer

Rewrite with a repeat loop: Initialize num=0, 'repeat', inside check if odd, print, increment num by 1 or 2, until num>=50.

Step-by-step solution

Understand the Original Code

The program initializes a variable `num` to 0. It then enters a `while` loop that continues as long as `num` is less than 50. Within the loop, when `num` is odd, it prints a statement indicating that `num` is odd, then increments `num` by 1. Regardless of whether it was odd or not, `num` is incremented by 1 again.

Analyzing Loop Condition and Iteration

Observe how the loop functions: it increments `num` twice during each loop (if `num` is odd) or once otherwise. Thus, every loop iteration increases `num` by 2 after potentially printing based on its odd nature.

Initialize Before Repeat Loop

Initialize `num` to 0 before the loop. This sets the starting point for the repeat-until loop, ensuring the same variables are used as in the original code.

Implement Repeat-Until Loop Structure

Replace the `while` loop with a repeat-until loop. This involves declaring a repeat loop, ensuring the body executes at least once, and setting the termination condition to stop when `num` reaches or exceeds 50.

Recreate Loop Logic Inside Repeat Loop

Inside the repeat loop, check if `num` is odd. If so, print the message 'num is Odd'. Increment `num` by 1 if it was odd, thus replicating the inside conditional incrementation. Increment `num` by an additional 1 at the end of each loop cycle to match the consistent incrementation of the original loop.

Set the Termination Condition

After completing a repeat-until cycle, ensure the loop continues until `num` is 50 or greater. The condition used in a repeat-until loop structure checks the opposite condition of a `while` loop, so ensure the loop iterates exactly when `num` is less than 50.

Key concepts

Loop Iteration

The concept of loop iteration is essential to understanding how loops work in programming. When you hear about loop iteration, think of it as each time a loop executes its body of code. In the context of the repeat-until loop structure, every iteration makes specific changes to the variables within it.

In our exercise, the loop body contains logic to determine if `num` is odd, outputs a message if true, and increments `num` by 1 or 2. Why 1 or 2? Because if `num` is odd, it first increases by 1 after printing a message, and then by another 1, so the increment within an iteration could be 2 in total.

Overall, each iteration of the loop involves:

• Checking a condition (if `num` is odd)
• Executing code based on that condition (printing)
• Changing the value of `num`

Repeating these steps ensures that `num` eventually grows large enough to meet a set termination condition, bringing the loop to an end.

Conditional Logic

Conditional logic is what makes programming adaptive and intelligent. In any given loop, conditions determine which paths the program will take. In many programs, such logic uses `if` statements to execute certain instructions when specified conditions are true.

In this exercise, the conditional logic is wrapped around the oddity of `num`. When `num` is odd, indicated by `num % 2 != 0`, a message "num is Odd" gets printed. This check is crucial because it directly influences whether the loop's behavior results in an output or just quietly increments a number.

In brief, conditional logic:

• Allows specific code blocks to run based on boolean expressions
• Ensures decisions are made within loops, like whether to show text
• Implements necessary checks to control program flow

Through conditions, the loop becomes more than just a mere counting machine; it behaves differently based on `num`'s characteristics, providing tailored functionality.

Program Initialization

Before any loop can begin, program initialization occurs. It's like preparing all necessary tools before starting a job. Initialization ensures programs have everything in place to function correctly.

For the repeat-until loop, initialization involves setting `num` to 0. This starting value is crucial because it sets the stage for all loop iterations and makes sure the loop's logic operates on known and consistent values. Without proper initialization, the rest of the program might not behave as intended, leading to logical errors or unexpected behavior.

During initialization:

• Variables are assigned starting values (like `num = 0`)
• The initial state of the program is determined
• Ensures seamless execution of subsequent code

Essentially, proper initialization is like laying a foundation before building a house. Everything that follows relies on this sturdy start, allowing the program to run smoothly and predictably.

Termination Condition

The termination condition is a critical part of any loop, determining when the loop should stop repeating. For programming loops, it's what ensures they don't run indefinitely, using up resources unnecessarily.

In the repeat-until structure, the condition is designed to stop looping once a certain criterion is met. In our exercise, the loop should terminate when `num` becomes 50 or greater. This is expressed as the condition, breaking free from the loop when no longer necessary to continue.

When setting a termination condition:

• Look for the point where further iterations aren't needed (e.g., when `num >= 50`)
• Ensure conditions reflect the opposite logic often seen in while loops
• Safeguard against infinite loops by verifying the condition's logic

This process ensures that the code not only performs its task efficiently but also respects system resources and time, stopping exactly when it's supposed to.