Question

include using namesp… # Consider the following program. What is its exact output? Show the values of the variables after each line executes, as in Example 6-13. #include using namespace std; void funOne(int& a); int main() { int num1, num2; num1 = 10; //Line 1 num2 = 20; //Line 2 cout << "Line 3: In main: num1 = " << num1 << ", num2 = " << num2 << endl; //Line 3 funOne(num1); //Line 4 cout << "Line 5: In main after funOne: num1 = " << num1 << ", num2 = " << num2 << endl; //Line 5 return 0; //Line 6 } void funOne(int& a) { int x = 12; int z; z = a + x; //Line 7 cout << "Line 8: In funOne: a = " << a << ", x = " << x << ", and z = " << z << endl; //Line 8 x = x + 5; //Line 9 cout << "Line 10: In funOne: a = " << a << ", x = " << x << ", and z = " << z << endl; //Line 10 a = a + 8; //Line 11 cout << "Line 12: In funOne: a = " << a << ", x = " << x << ", and z = " << z << endl; //Line 12 }

Short answer

Line 3: In main: num1 = 10, num2 = 20 Line 8: In funOne: a = 10, x = 12, and z = 22 Line 10: In funOne: a = 10, x = 17, and z = 22 Line 12: In funOne: a = 18, x = 17, and z = 22 Line 5: In main after funOne: num1 = 18, num2 = 20

Step-by-step solution

Initialization in main

After Line 1, `num1` is initialized to 10. After Line 2, `num2` is initialized to 20. After Line 3, the console outputs "Line 3: In main: num1 = 10, num2 = 20".

Entering funOne function

Line 4 calls `funOne` with `num1` as the argument, thus passing 10 by reference to `a`. Inside `funOne`, `x` is initialized to 12 before executing Line 7.

Calculations in funOne

At Line 7, `z` is assigned the value of `a + x`, which is `10 + 12 = 22`. After this, Line 8 outputs "Line 8: In funOne: a = 10, x = 12, and z = 22".

Modify x in funOne

At Line 9, `x` is incremented by 5, making `x = 17`. After this, Line 10 outputs "Line 10: In funOne: a = 10, x = 17, and z = 22".

Modify a in funOne

At Line 11, `a` (which references `num1`) is incremented by 8, resulting in `a = 18` (thus `num1` is also 18). After this, Line 12 outputs "Line 12: In funOne: a = 18, x = 17, and z = 22".

Return to main

After returning from `funOne`, Line 5 outputs the updated value of `num1` as "Line 5: In main after funOne: num1 = 18, num2 = 20".

Key concepts

Pass by Reference

In C++, passing by reference is a way to give functions the ability to modify the argument passed to them. It is achieved by using the ampersand symbol (&) as shown in the function declaration.

• When a variable is passed by reference, its memory address is used.
• Changes inside the function directly affect the original variable.

In the given exercise, the line `void funOne(int& a);` demonstrates passing by reference. Here, `num1` is passed to `funOne` as `a`. Any modifications made to `a` within `funOne` will change `num1` in the `main` function, as seen when `a` is increased by 8 and `num1` becomes 18. Passing by reference is especially useful when you want to avoid copying large amounts of data or need to modify the original data.

Variable Initialization

Variable initialization is the process of assigning an initial value to a variable at the point of its creation. This ensures that variables start with a known value and helps avoid unexpected behavior or errors. In the provided exercise:

• `int num1, num2;` declares two integer variables without initializing them.
• `num1 = 10;` and `num2 = 20;` initialize these variables, giving them the values 10 and 20, respectively.

Skipping initialization could lead to variables containing garbage values, which can lead to bugs. By initializing a variable upon its creation or directly after, you establish a baseline state and improve the predictability of your program. Remember, when a function parameter is passed by reference, like `a`, its initial state is the current state of the variable being referenced, which is `num1` in this case.

Console Output

Console output in C++ allows programs to display results or messages to the screen, providing a way to communicate with the user or developer. In C++, `std::cout` is used to print text or variables to the console. The operator `<<` is known as the insertion operator and is used to send output to the console. Example from the Exercise:

• Line 3: `cout << "Line 3: In main: num1 = " << num1 << ", num2 = " << num2 << endl;` prints the initial values of `num1` and `num2`.
• Inside `funOne`, multiple `cout` statements show changes to variables as operations occur.

Using console output is crucial in debugging, as it can reveal real-time data changes and ensure the code behaves as expected. Don't forget to use `endl` to ensure each message ends with a newline, making the output more readable.

Function Parameters

Function parameters play a significant role in determining how data is passed into functions and how that data is manipulated.

• Parameters provide a way to input data into functions, allowing them to operate on this data and potentially return a result.
• They include regular parameters (passed by value) and reference parameters (passed by reference).

In the given exercise, the function `funOne` uses a reference parameter `int& a`. This means the actual variable `num1` is manipulated within `funOne`, instead of a copy. Choosing the right type of parameter is essential:

• **Pass by value** is used when you don't need to modify the original data.
• **Pass by reference** is for cases where modifications are required or to save memory with large objects.

Function parameters enhance code modularity and reusability, enabling functions to be more flexible in handling different data inputs.