Question

include using namespace std; void find(int a, int& b, int& c); int main() { int one, two, three; one = 5; two = … # What is the output of the following program? #include using namespace std; void find(int a, int& b, int& c); int main() { int one, two, three; one = 5; two = 10; three = 15; find(one, two, three); cout << one << ", " << two << ", " << three << endl; find(two, one, three); cout << one << ", " << two << ", " << three << endl; find(three, two, one); cout << one << ", " << two << ", " << three << endl; find(two, three, one); cout << one << ", " << two << ", " << three << endl; return 0; } void find(int a, int& b, int& c) { int temp; c = a + b; temp = a; a = b; b = 2 * temp; }

Short answer

The program outputs: 5, 10, 15; 5, 10, 15; 25, 30, 15; 25, 30, 20.

Step-by-step solution

Understanding Variable Assignments

In the `main` function, we have three integer variables initialized: `one` is set to 5, `two` to 10, and `three` to 15. The function `find` is called with these variables in different sequences in four different calls.

Analyzing the find Function

The `find` function takes three arguments: an integer by value, `a`, and two integers by reference, `b` and `c`. Inside the function, `c` is updated to be the sum of `a` and `b`. Then, `a` is assigned to a temporary variable `temp`. Next, `a` is updated to the value of `b`, and `b` is updated to `2 * temp`.

First Call to find(one, two, three)

In `find(one, two, three)`, `a = 5`, `b = 10`, `c = 15`. `c` becomes `5 + 10 = 15`. Then `temp = 5`, afterwards, `a` becomes `10` and `b` becomes `2 * 5 = 10`. However, since `a` is passed by value, changes to `a` don't affect `one`. Thus, the variables remain `one = 5`, `two = 10`, and `three = 15`.

Second Call to find(two, one, three)

Now, `a = 10`, `b = 5`, `c = 15`. `c` is updated to `10 + 5 = 15`. After storing `10` in `temp`, `a` becomes `5`, and `b` becomes `2 * 10 = 20`, but these changes don't affect the original variables `two`, `one`, and `three`. The variables remain `one = 5`, `two = 10`, `three = 15`.

Third Call to find(three, two, one)

Here, `a = 15`, `b = 10`, `c = 5`. `c` is updated to `15 + 10 = 25`. Then `a` is stored in `temp`, so `temp = 15`. Then, `a` is set to `10`, and `b` becomes `2 * 15 = 30`. Since `a` is passed by value, `three` is unaffected. The variables are `one = 5`, `two = 30`, `three = 15`.

Fourth Call to find(two, three, one)

In this call, `a = 10`, `b = 15`, `c = 5`. `c` becomes `10 + 15 = 25`. Temporary stores `10`. Now, `a` becomes `15`, and `b` is updated to `2 * 10 = 20`. `a` being by value leaves `two` unchanged: `one = 25`, `two = 30`, and `three = 20`.

Compile Program Output

Compile all results gathered from each call within the `main()` function. The output after each `cout` is: 1. `5, 10, 15` 2. `5, 10, 15` 3. `25, 30, 15` 4. `25, 30, 20`.

Key concepts

Pass by Reference

In C++, **Pass by Reference** is a method of passing arguments to a function simply by using references. This allows the function to modify the actual variables passed to it, rather than just working on a copy.
When a parameter is passed by reference, it uses the ampersand (`&`) symbol next to the variable type. For instance, in the `find` function, `b` and `c` are passed by reference (`int& b, int& c`).
**Benefits:**

• Allows direct modification of the variable's value in the calling function.
• Efficient for large data structures since no copies are made.

In the exercise, you can observe that changes to `b` and `c` inside `find` affect the actual variables in `main`, but `a` remains unchanged because it's passed by value.

Variable Scope

**Variable Scope** determines which parts of a program can access certain variables, affecting both understanding and functionality.
In C++, there are primarily two types of scope:

• **Local Scope:** Variables like `temp` in the `find` function are local. They are accessible only within the function where they are declared.
• **Global Scope:** Variables available throughout the program across different functions, but not used in this particular exercise.

The variables `one`, `two`, `three` are local to `main`. They are only accessible within `main`. Understanding scope helps in managing and avoiding conflicts between variable names.

Function Parameters

**Function Parameters** define what inputs a function expects to receive in order to perform its operations.
When defining a function, you specify its parameters in the parameter list which comes after the function name. In our case, the `find` function has three parameters: `int a`, `int& b`, and `int& c`.

• **By Value (`int a`):** The function works with a copy of the argument passed, safeguarding the original variable from modifications.
• **By Reference (`int& b`, `int& c`):** These parameters let the function directly alter the variables, making it flexible for various tasks.

A function's parameter list is crucial as it dictates how data is transferred and manipulated, and understanding the difference between reference and value is key to effective function use in C++.