Question

What is the output of the following C++ code? int num = 1; while (num < 10) { cout << num << " "; num = num + 2; } cout << endl;

Short answer

Output: 1 3 5 7 9

Step-by-step solution

Initialize the Variable

The variable `num` is initialized with the value 1 at the start of the program. This initial value will be used in the while loop condition.

Analyze the While Loop Condition

The while loop will continue executing as long as the condition `num < 10` holds true. Initially, `num` is 1, which satisfies the condition.

First Iteration of the Loop

In the first iteration, since `num` is 1, the program prints "1 ". Then, `num` is incremented by 2, making `num = 3`.

Second Iteration of the Loop

With `num` now at 3, the condition `num < 10` is still true. The program prints "3 ". Afterwards, `num` becomes 5 after adding 2.

Third Iteration of the Loop

Now, `num` is 5, so the program prints "5 ". Then, `num` is increased to 7 after adding 2.

Fourth Iteration of the Loop

For `num = 7`, the condition is true. The program prints "7 ". Incrementing `num` by 2 results in `num = 9`.

Fifth Iteration of the Loop

Now, `num` is 9. The program prints "9 ". Adding 2 gives `num = 11`.

Examine Loop Exit Condition

After the increment, `num` becomes 11, which does not satisfy `num < 10`. Therefore, the loop exits.

Print Final Output

Once the loop is exited, a new line is printed via `cout << endl;`. This completes the program's execution.

Key concepts

Control Structures

In programming, control structures guide the execution flow of a program. In C++, as in many other languages, we have a variety of control structures like loops, conditionals, and branches. These structures determine how the code is executed, affecting whether certain segments are run or skipped.

A `while` loop is a type of control structure that repeatedly executes a block of code as long as a provided condition remains true. This allows for efficient handling of tasks that need repetition, such as processing items in a list or counting from one to ten. It helps to reduce code redundancy and improve maintainability.

In our example code, the `while` loop checks a condition before executing. The loop's condition is the cornerstone of its functionality, controlling how many times the code within it will run.

Increment Operation

Increment operations are a common element inside loops, especially in scenarios where the loop must progress toward a termination condition.

In C++, incrementing means increasing the value of a variable by a specific amount, typically by 1. However, you can increment by any number depending on the requirement. In the context of our example, using `num = num + 2` increases the variable `num` by 2 with each iteration.

This operation is critical to ensuring that eventually the loop will stop running. Without incrementing `num`, the loop condition might always remain true, causing an infinite loop. Efficiently using increment operations allows developers to manage loops effectively and create precise control over the number of iterations.

Loop Condition

The loop condition serves as the gatekeeper for loops. It is a Boolean expression evaluated before (or during in some loop types) each iteration. As long as this condition returns true, the loop continues to execute. In our C++ example, the condition is `num < 10`.

This condition signifies that as long as `num` is less than 10, the loop's code block will keep running. Once `num` reaches a value of 10 or more due to the increment operation, the condition becomes false, and the loop exits.

Choosing and setting the correct loop condition is vital. It determines the loop's lifecycle - how long it will run and when it should terminate. Careful consideration of these conditions helps prevent erroneous or infinite loops, making sure the program runs smoothly as intended.

Loop Iterations

Each time the code inside a loop executes, it is called an iteration. In our example, the loop begins with `num` set at 1 and performs several iterations until the condition `num < 10` is no longer met.

For each iteration:

• The current value of `num` is printed.
• `num` is incremented by 2.
• The loop checks if the incremented value still satisfies the loop condition.

By understanding iterations, we can predict the flow and outcome of loops. Knowing how many iterations will occur and what actions are performed in each is crucial for debugging and optimizing code.

In our case, this loop prints the sequence `1 3 5 7 9`, where each number is an iteration outcome showing how `num` changes through successive additions.