Question

include using namespace std; void tryMe(int& v); int main() { int x = 8; for (int count = 1; count < 5; count++)… # What is the output of the following program? #include using namespace std; void tryMe(int& v); int main() { int x = 8; for (int count = 1; count < 5; count++) tryMe(x); return 0; } void tryMe(int& v) { static int num = 2; if (v % 2 == 0) { num++; v = v + 3; } else { num--; v = v + 5; } cout << v << ", " << num << endl; }

Short answer

The output is: 11, 3 16, 2 19, 3 24, 2

Step-by-step solution

Initialization

We start by analyzing the `main()` function. This function initializes an integer `x` with a value of 8 and sets up a `for` loop with a counter `count` that runs from 1 to 4 (since `count < 5`). Each iteration of this loop calls the function `tryMe(x)` where `x` is passed by reference.

Function Behavior

The `tryMe(int& v)` function uses a static variable `num`, initialized to 2. The static variable retains its value between function calls. The function checks if `v` (which is `x` as it's passed by reference) is even.

First Loop Iteration

Initially, `x` is 8, which is even. Inside `tryMe`, since `x % 2 == 0`, `num` is incremented to 3, and `x` is increased by 3, resulting in `x = 11`. The function prints `11, 3`.

Second Loop Iteration

Now, `x` is 11, which is odd. The function now decrements `num` to 2, and then increases `x` by 5, making `x = 16`. It prints `16, 2`.

Third Loop Iteration

With `x = 16` (even), `num` is incremented to 3, and `x` is increased by 3, resulting in `x = 19`. The output is `19, 3`.

Fourth Loop Iteration

Finally, `x` is 19, which is odd. `num` is decremented back to 2, and `x` is increased by 5, resulting in `x = 24`. The function prints `24, 2`.

End of Loop

The `for` loop has completed its iterations (1 through 4), and `main()` concludes with `return 0`, terminating the program.

Key concepts

Understanding Control Structures in C++

Control structures in C++ are essential tools that allow you to dictate the flow of a program. Think of them as the basic building blocks, which help the program make decisions and execute specific blocks of code based on certain conditions. Common control structures include loops and conditionals.

In the provided exercise, a `for` loop is used as a control structure to repeat a block of code multiple times. Specifically, the loop runs from 1 to 4 (due to `count < 5` condition). Each iteration calls the `tryMe()` function. Here’s a simple breakdown:

• The loop initializes with `count = 1`.
• It checks if `count < 5`, if true, the loop body executes.
• After executing, `count` is incremented and the condition is checked again.

Such structures are very powerful in automating repetitive tasks without manually writing out every step.

Functions in C++

In C++, functions are reusable blocks of code designed to perform a specific task. They help in breaking down the program into smaller, manageable sections, enhancing readability and organization.

The `tryMe(int& v)` function from the exercise is a custom function that takes one parameter. This parameter is passed by reference (we'll explore more about this later). The key parts of a function include its name, return type, and parameters.

Functions encapsulate logic, allowing us to apply the same operation multiple times. In the exercise, the logic for modifying the variable `x` and printing the results is all contained within `tryMe`. This keeps the main part of the program clean and focused on high-level flow.

Embracing Static Variables

Static variables in C++ are unique because they retain their value between function calls. Unlike regular local variables which get destroyed and reinitialized every time a function is called, static variables preserve their state.

In the `tryMe()` function, `num` is declared as static. This means:

• It is only initialized once, the first time the function is called, setting `num` to 2.
• On subsequent calls, it retains the value it had from the previous call.

This characteristic makes static variables ideal for counting occurrences, maintaining states, or caching results without using global variables. In the exercise, `num` helps track alterations across different invocations, influencing the output behavior dynamically.

Pass-by-Reference Explained

Pass-by-reference is a parameter passing method where the actual memory address of the argument is passed to the function. This means any changes made to the parameter will affect the actual argument. In our exercise, the function `tryMe(int& v)` receives variable `x` by reference. The `&` symbol is crucial here and signifies that `v` is a reference to `x`. Thus, modifications within `tryMe`, such as incrementing `x` or changing it, are directly reflected in `x` in `main()`.

Benefits of pass-by-reference include:

• Memory efficiency, as no copy of the variable is made.
• Able to modify the original variable, which can be useful in specific situations where this behavior is desired.

In this program, pass-by-reference is cleverly used to update the value of `x` across multiple function calls.