Question

What is the output of the following program segment? int count = 0; while (count++ < 10) cout << "This loop can repeat statements." << endl;

Short answer

The output is printed 10 times.

Step-by-step solution

Initialize Count

The program initializes an integer variable named `count` and sets it to 0. This variable will be used to control the loop execution.

Execute the Loop

The program enters a `while` loop with the condition `count++ < 10`. This means that the current value of `count` is checked to be less than 10, and then `count` is incremented by 1 after the check.

Evaluate Loop Condition

Initially, `count` is 0. The loop checks if 0 < 10, which is true, so the loop executes its body. After the loop body executes, `count` becomes 1 because of the post-increment `count++`. This process repeats with `count` incrementing to 2, 3, and so forth, as long as `count` before incrementing is less than 10.

Execute Loop Body

For each iteration where the condition is true, the loop prints the string `"This loop can repeat statements."`. Since the loop runs when `count` is 0 through 9 (10 iterations in total), this statement is printed 10 times.

End of Loop Execution

When `count` reaches the value of 10 after post-increment, the condition `count++ < 10` becomes false (since it checks `10 < 10`), so the loop ends without executing its body. Thus, the statement has been printed 10 times.

Key concepts

Post-Increment Operator

In C++, the post-increment operator is represented by `++` following a variable name, like `count++`. This operator plays an important role by incrementing the variable's value but not before the value is used in an expression. When you have an expression such as `count++ < 10`, the current value of `count` is first compared with 10. Only after this comparison does `count` increase by one.

The difference between post-increment (`count++`) and pre-increment (`++count`) is key. In `count++`, the variable is assessed in its current state before the operation adds one, while with `++count`, the increment occurs before the operation assessing the variable takes place. Knowing when these increments happen ensures a clear prediction of how your program behaves at each step.

Loop Condition

The loop condition in a `while` loop determines whether the loop's body should execute again. In this exercise, the loop condition is `count++ < 10`. It checks if `count` is less than 10, and if true, the loop's body executes.

Because of the post-increment operator, the condition `count++ < 10` checks `count` at its initial value during each iteration, before increasing its value by 1. Understanding this sequence is crucial to predicting how many times the loop will run. This loop will continue to execute as long as the evaluated value of `count` (before increment) is less than 10.

Loop Body Execution

The loop body is the part of a loop that executes repetitively while the condition remains true. In this example, the loop body contains a single command: `cout << "This loop can repeat statements." << endl;`. This statement is executed each time the loop condition is satisfied.

Since the loop starts with count at 0 and the condition checks `count < 10`, the statement executes repeatedly for each value of `count` from 0 to 9 inclusive. This means the body executes a total of 10 times—each time printing the message to the standard output. It is crucial to understand this repeated execution to grasp loop mechanics fully.

Program Output Analysis

Understanding the output of a program segment requires examining how often the loop body executes based on its condition. In the provided exercise, the loop's output is determined by the number of times the condition `count++ < 10` held true.

For each value of `count` starting from 0 and up to 9, the loop condition evaluates as `true`, leading the loop to print the statement "This loop can repeat statements." on each iteration. Thus, the entire phrase outputs on 10 separate lines. Each iteration results from the loop body's execution contingent on the loop's condition being true. When `count` increments to 10 due to the post-increment operation, the condition evaluates to `false`, causing the loop to terminate and ceasing further outputs.