Question

include using namespace std; int x; void summer(int&, int); void fall(int, int&); int main() { int intNum1 = 2; … # What is the output of the following program? #include using namespace std; int x; void summer(int&, int); void fall(int, int&); int main() { int intNum1 = 2; int intNum2 = 5; x = 6; summer(intNum1, intNum2); cout << intNum1 << " " << intNum2 << " " << x << endl; fall(intNum1, intNum2); cout << intNum1 << " " << intNum2 << " " << x << endl; return 0; } void summer(int& a, int b) { int intNum1; intNum1 = b + 12; a = 2 * b + 5; b = intNum1 + 4; } void fall(int u, int& v) { int intNum2; intNum2= x; v = intNum2 * 4; x = u - v; }

Short answer

The program outputs: First: `15 5 6` Second: `15 24 -9`.

Step-by-step solution

Understand the Main Function Initial Values

In the `main()` function, two integers `intNum1` and `intNum2` are initialized to 2 and 5 respectively. The global variable `x` is set to 6.

Analyze the Function "summer"

The `summer` function takes two parameters, an integer reference `a` and an integer `b`. Inside `summer`, `a` is changed to `2 * b + 5`, which equals `2 * 5 + 5 = 15`. It also calculates a local variable, `intNum1`, which equals `b + 12`, and sets `b = intNum1 + 4 = 21`. Since `b` is passed by value, changes to `b` do not affect `intNum2` in `main`.

First Output after "summer"

After calling `summer(intNum1, intNum2)`, `intNum1` becomes 15. `intNum2` remains 5 because `b` in `summer` is a local copy. The value of `x` remains unchanged at 6. Therefore, the output is `15 5 6`.

Analyze the Function "fall"

The `fall` function takes an integer `u` and an integer reference `v`. Inside, a local `intNum2` is assigned the current `x` which is 6. `v` is then updated to `intNum2 * 4 = 24`. `x` is updated to `u - v = 15 - 24 = -9`. Thus, `intNum2` becomes 24 but `intNum1` is unchanged in memory.

Second Output after "fall"

After calling `fall(intNum1, intNum2)`, `intNum1` remains 15 and `intNum2` is now 24. The global `x` is updated to -9. Therefore, the output is `15 24 -9`.

Key concepts

Reference Parameters

In C++, reference parameters are used when you want a function to modify the argument passed to it.
Instead of passing a copy of the variable's value, a reference to the actual variable is passed.
This allows the function to make changes to the original variable.

• Syntax: When declaring a function, reference parameters are indicated by adding an ampersand (&) after the data type.
• Example: In the `summer` function, `int& a` is a reference parameter. This means any changes to `a` inside the function will be reflected in the actual variable passed from the caller.
• Benefit: This method saves memory because no new copy of the variable is made. It's particularly useful for large data structures.

In the provided exercise, the `summer` function alters `intNum1` directly through its reference parameter `a`, turning its value to 15.
On the other hand, the `fall` function uses `v` as a reference parameter, modifying `intNum2` to 24.

Value Parameters

Value parameters are another way to pass arguments to a function.
When you use value parameters, a copy of the variable is made and used inside the function.
The original variable remains unchanged, as only the copy is modified.

• Example: In the `summer` function, `int b` is a value parameter. Changes made to `b` within the function do not affect `intNum2` in the `main()`.
• Usage: Useful when you want to ensure the original variable remains unaffected by the operations conducted within the function.
• Drawback: More memory is used since a duplicate is created, which is negligible with simple data types but becomes significant with large structures.

In the given problem, even though `b` in the `summer` function changes, `intNum2` stays the same, illustrating the immutability of the original variable with value parameters.
The initial value of 5 for `intNum2` remains unchanged after executing `summer(intNum1, intNum2)`.

Global Variables

A global variable has its scope throughout the entire program and can be accessed by any function.
Declaring a variable globally means it is stored in the program's global memory,

• Example: In the exercise, `x` is declared globally above the main function. It's accessible in both `summer` and `fall` functions.
• Pros: It provides ease of access to a single variable from multiple locations in code.
• Cons: Overusing global variables makes tracking changes difficult, potentially leading to issues such as unexpected results and reduced code clarity.

In this problem, `x` begins with a value of 6, remains unchanged by `summer`, and then is modified to -9 in the `fall` function, since global variables retain their values and changes across different function calls.

Function Analysis

Analyzing functions allows us to understand how data is manipulated and transferred.
In the given code, each function alters specific values differently based on C++ parameter passing methods.

• The `summer` function multiplies the reference parameter `a` and modifies it directly while using `b` without affecting its original value.
• The `fall` function takes `u` as a value parameter and `v` as a reference parameter. Its actions modify `v` and `x`, based on the initial values they receive.
• Output: Gathering these observations can help predict outputs after function executions, such as `15 5 6` post-summer and `15 24 -9` post-fall.

By systematically analyzing how parameters are passed and altered through each function, we arrive at a clearer understanding of how C++ handles data
and how each of these constructs contributes to the overall functionality and result of a program.