Question

Given the following program segment: for (number = 1; number <= 10; number++) cout << setw(3) << number; write a while loop and a do...while loop that have the same output.

Short answer

Convert the loop to both while and do...while with correct syntax to produce the same output.

Step-by-step solution

Understand the Problem

The for loop provided iterates over numbers from 1 to 10 and prints each number with a width of 3. We need to replicate this behavior using a while loop and a do...while loop.

Write the While Loop

Begin by initializing the `number` variable to 1 before entering the while loop. Then, use the while condition to check if `number` is less than or equal to 10. Inside the loop, print the `number` and increase its value by 1 after printing. The loop will continue until `number` exceeds 10. ``` int number = 1; while (number <= 10) { cout << setw(3) << number; number++; } ```

Write the Do...While Loop

Initialize the `number` variable to 1. In a do...while loop, execute the printing and increment logic first, and then check the condition. This ensures that the loop executes at least once. Print the `number`, increment it by 1, and continue the loop until `number` is greater than 10. ``` int number = 1; do { cout << setw(3) << number; number++; } while (number <= 10); ```

Key concepts

for loop

The `for loop` is a fundamental concept in programming languages like C++, where actions must be repeated a predefined number of times. It provides a concise way to accomplish iteration. The syntax of a `for loop` typically consists of three main parts:

• Initialization: This sets the initial state. In our example, it is number = 1.
• Condition: This is checked before each iteration. The loop continues as long as this condition is true. For instance, number <= 10.
• Update: After each iteration, this part updates the state. In the provided example, this is number++, which increments the value by 1.

The flexibility of the `for loop` lies in its structure. It combines the initialization, condition-checking, and update steps in one line, making the loop easy to understand for short to moderate repetitions. Its design excels in cases where the number of iterations is known upfront.

while loop

A `while loop` is another important type of loop in C++. It functions by repeatedly executing a block of code as long as the specified condition remains true. Here's how you can understand it:

• Initialization: Similar to the `for loop`, you need to initialize any variables outside the loop. In our rewritten example, int number = 1; establishes the starting point before the loop begins.
• Loop Condition: The condition number <= 10 is checked before each loop execution. If it evaluates to false, the loop terminates.
• Body Execution: Within the loop body, the required actions—like cout << setw(3) << number;—are executed if the condition is true.
• Update: After executing the loop body, you must manually update the variable (e.g., number++;), ensuring the loop progresses toward completion.

A `while loop` is particularly useful when the number of iterations isn't known beforehand and conditions dictate when the loop should stop, offering more flexibility in certain scenarios.

do...while loop

The `do...while loop` in C++ resembles the `while loop` but with a key difference: it guarantees at least one execution of the loop body. The control flow works as follows:

• Initialization: As with other loops, initialize your loop variable outside the loop. In our case, int number = 1; is set initially.
• Loop Execution: The loop executes the body first, executing statements such as cout << setw(3) << number;, and then modifies the state with number++;.
• Condition Evaluation: After executing the loop body, the condition (number <= 10) is evaluated. If it's true, the process repeats.

The `do...while` loop is particularly useful when the loop body needs to be executed at least once, regardless of whether the condition is initially true. This ensures that the loop actions occur before the first condition check, providing a slight difference in control compared to other loop structures.