Question

Consider the following function definition: void defaultParam(int num1, int num2 = 7, double z = 2.5) { int num3; num1 = num1 + static_cast(z); z = num2 + num1 * z; num3 = num2 - num1; cout << "num3 = " << num3 << endl; } What is the output of the following function calls? a. defaultParam(7); b. defaultParam(8, 2); c. defaultParam(0, 1, 7.5); d. defaultParam(1, 2, 3.0);

Short answer

-2, -8, -6, -2.

Step-by-step solution

Understand Default Parameters

The function "defaultParam" has three parameters: 1. \( \text{num1} \) which takes the input value. 2. \( \text{num2} \) which defaults to \( 7 \) if not provided. 3. \( z \) which defaults to \( 2.5 \) if not provided.

Evaluate Call a: defaultParam(7)

For this call, \( \text{num1} = 7 \), \( \text{num2} = 7 \) (default), and \( z = 2.5 \) (default). - Calculate new \( \text{num1} \): \( num1 = 7 + 2 = 9 \)- Calculate new \( z \): \( z = 7 + 9 \times 2.5 = 29.5 \)- Calculate \( \text{num3} \): \( num3 = 7 - 9 = -2 \) - Output: "num3 = -2".

Evaluate Call b: defaultParam(8, 2)

For this call, \( \text{num1} = 8 \), \( \text{num2} = 2 \), and using the default \( z = 2.5 \). - Calculate new \( \text{num1} \): \( num1 = 8 + 2 = 10 \)- Calculate new \( z \): \( z = 2 + 10 \times 2.5 = 27 \)- Calculate \( \text{num3} \): \( num3 = 2 - 10 = -8 \) - Output: "num3 = -8".

Evaluate Call c: defaultParam(0, 1, 7.5)

For this call, \( \text{num1} = 0 \), \( \text{num2} = 1 \), and \( z = 7.5 \). - Calculate new \( \text{num1} \): \( num1 = 0 + 7 = 7 \) - Calculate new \( z \): \( z = 1 + 7 \times 7.5 = 53.5 \) - Calculate \( \text{num3} \): \( num3 = 1 - 7 = -6 \) - Output: "num3 = -6".

Evaluate Call d: defaultParam(1, 2, 3.0)

For this call, \( \text{num1} = 1 \), \( \text{num2} = 2 \), and \( z = 3.0 \).- Calculate new \( \text{num1} \): \( num1 = 1 + 3 = 4 \)- Calculate new \( z \): \( z = 2 + 4 \times 3.0 = 14 \)- Calculate \( \text{num3} \): \( num3 = 2 - 4 = -2 \)- Output: "num3 = -2".

Key concepts

Function Overloading

Function overloading in C++ is a powerful feature that allows you to use the same function name multiple times with different argument lists. This means that each function version has a different parameter type or a different number of parameters. When you call an overloaded function, the compiler determines which version of the function to invoke based on the arguments you provide.
This is particularly useful when you want to perform similar operations on different data types, and it helps improve code readability by reducing the number of distinctly named functions.
For example, you might have a function to calculate the area of different shapes like a circle or square, and overloading lets you use the same function name while catering to different parameters. Function overloading offers flexibility, allowing functions to be called with a variety of argument lists, while the appropriate function gets matched during compilation.

Parameter Passing

Parameter passing is about how arguments are given to functions and how they are handled in the context of that function. In C++, there are several methods of passing parameters:

• Pass by Value: A copy of the actual argument is passed to the function, meaning modifications to the parameter inside the function have no effect on the actual argument.
• Pass by Reference: The function receives a reference to the actual argument, allowing changes within the function to affect the original variable.
• Pass by Pointer: Similar to pass by reference, but it involves pointers, giving the function a pointer to the actual argument. It offers more flexibility but requires careful memory management.

In the given exercise function "defaultParam," parameters are passed by value. As such, changes within the function do not affect any variables outside of it, demonstrating how local computations are independent of external variables.

Type Casting

Type casting in C++ is the method of converting a variable from one data type to another. It is crucial when you are performing operations on different data types to ensure they are compatible with one another. C++ supports two primary types of casting: implicit and explicit.

• Implicit Type Casting: Also known as automatic type conversion, where the compiler converts data types for operations that need a consistent type.
• Explicit Type Casting: Requires the programmer to specify the type conversion using casting operators, ensuring precision control. An example is the use of static_cast, which is a safer way to perform conversions.

In the exercise, the "defaultParam" function uses `static_cast(z)` for explicit type conversion from the floating point to an integer. This is necessary because operations within the function may need integer-type conversion for mathematical operation on `num1`.

Function Calls Evaluation

Evaluating function calls involves determining the order and the correct values with which parameters are passed into the function. This includes employing default parameter values when certain arguments are not provided.
In C++, when a function is called, the order of evaluation for each argument follows the parameter list position. Default parameters play a part when specific arguments are omitted, filling in with predefined values.
In the exercise, `defaultParam` demonstrates how evaluations occur when function calls lack parameters since defaults are then used. Each call in the exercise evaluates differently based on which arguments are given and which defaults apply, showcasing how default parameters can simplify and standardize function calls. The varied outputs from different calls highlight how critical it is to pay attention to the presence of defaults and properly evaluate the order and values of provided and default parameters.