Question

What is the output of the following program segment? int count \(=1 ;\) while \((\operatorname{count}++<=5)\) cout \(<<\) count \(\star(\text { count }-2)<<\cdots\) " cout \(<<\) endl

Short answer

The output is '0 3 8 15 24' followed by a newline.

Step-by-step solution

Initialize Variables

The program starts by initializing an integer variable 'count' to 1. This sets up our loop by establishing a starting value for 'count'.

Evaluate Loop Condition

The while loop checks the condition \(\text{count}++ <= 5\). This means it will compare 'count' with 5, then increment 'count' by 1 immediately after the comparison.

First Iteration

In the first iteration, 'count' is 1, and the condition evaluates true since 1 <= 5. After the condition check, 'count' becomes 2, and the expression after 'cout' calculates as \(2 \times (2-2) = 0\), so it prints '0'.

Subsequent Iterations

The process repeats: - For 'count' initially 2, the condition checks if 2 <= 5, which is true. 'count' increases to 3, and \(3 \times (3-2) = 3\) is printed.- For 'count' initially 3, it checks if 3 <= 5, so 'count' increases to 4, and \(4 \times (4-2) = 8\) is printed.- For 'count' initially 4, it checks if 4 <= 5, so 'count' increases to 5, and \(5 \times (5-2) = 15\) is printed.- For 'count' initially 5, it checks if 5 <= 5, so 'count' increases to 6, and \(6 \times (6-2) = 24\) is printed.

Loop Termination and Output of New Line

Now, 'count' becomes 6, and the condition 6 <= 5 becomes false, thus exiting the loop. Then, 'cout << endl' outputs a newline character.

Key concepts

Understanding Increment Operators

Increment operators are essential in programming, especially when dealing with loops. In C++, the increment operator `++` can be used to increase the value of a variable by 1. It can be placed either before or after a variable, and this placement affects how the operation is performed and when the value is updated.

• Post-increment (e.g., count++): The variable is used in an expression and then incremented. The original value is returned before incrementing.
• Pre-increment (e.g., ++count): The variable is incremented first, and then the updated value is used in an expression.

In our program, `count++` is a post-increment operation, meaning each comparison in the loop uses the current value of `count`, and then `count` is incremented.
This subtlety significantly affects how the loop operates, as you can observe with the printed output changing based on the immediate increment after evaluation.

Loop Conditions in C++

Loop conditions are crucial for controlling the execution of loops in C++. They determine how many times and under what circumstances the loop will run. In our exercise, we have a `while` loop with the condition `count++ <= 5`.
A while loop keeps executing as long as the condition evaluates to true. Here, the loop keeps running while the current value of `count` is less than or equal to 5. The post-increment operation means `count` is checked first, then incremented.

• Initialization: Before entering the loop, `count` is initialized to 1, setting the stage for condition checks.
• Condition Check: Before each iteration, the condition is verified. If true, the loop executes; otherwise, it exits.

This condition ensures that the loop's operations occur precisely five times, as each check reflects `count`'s current state before incrementing it.

Loop Iteration Process

A loop iteration in C++ refers to a single cycle through the loop, where the block of code within the loop executes once. In our example, the loop iterates five times because the `while` condition uses a `count` value from 1 to 5.
During each iteration:

• The loop evaluates whether to execute based on the condition.
• `count` is used in the expression for printing, a calculation occurs, and then it prints the result.
• After printing, `count` increases as per the increment operator used in the loop condition.

This predictable process allows us to understand how each iteration yields the output seen in the program, and demonstrates the controlled flow of executing repetitive tasks.

Using cout for Output

In C++, `cout` is used to display output on the console. It's part of the iostream library and is fundamental for interacting with the user or showing results of computations.
The syntax for using `cout` is straightforward. It utilizes the insertion operator `<<` to stream data to the console. For instance, `cout << count` will output the current value of `count`.

• Chaining Outputs: `cout` can be chained to output multiple variables or strings in one command, like `cout << a << b`.
• End of Output: To move to a new line after outputting, `endl` can be used with `cout`, ensuring readability in console outputs.

In our program segment, `cout << endl` at the end effectively adds a newline, making the final console output clearer and easier to read.