Question

Perform the task specified by each of the following statements: a. Write the function header for a function called exchange that takes two pointers to double-precision, floating-point numbers x and y as parameters and does not return a value. b. Write the function prototype for the function in part (a). c. Write the function header for a function called evaluate that returns an integer and that takes as parameters integer x and a pointer to function poly. Function poly takes an integer parameter and returns an integer. d. Write the function prototype for the function in part (c). e. Write two statements that each initialize character array vowel with the string of vowels, "AEIOU".

Short answer

The function header for 'exchange' is `void exchange(double* x, double* y)`; header for 'evaluate' is `int evaluate(int x, int (*poly)(int))`; vowel initialization can be `char vowel[] = "AEIOU";`.

Step-by-step solution

Writing Function Header for 'exchange'

To write the function header for a function called 'exchange', which takes two pointers to double-precision floating-point numbers as parameters and returns nothing, we must specify the name, parameter types, and indicate no return with 'void'. This leads us to the header: \[ \text{void exchange(double* x, double* y)} \]

Writing Function Prototype for 'exchange'

The function prototype provides a declaration of the function before its definition. It specifies the return type, the function name, and the parameter types, but does not include the function body. For 'exchange', the prototype is: \[ \text{void exchange(double* x, double* y);} \]

Writing Function Header for 'evaluate'

In the function 'evaluate', it returns an integer and takes an integer \(x\) and a pointer to function 'poly', which itself takes an integer parameter and returns an integer. The header is written as:\[ \text{int evaluate(int x, int (*poly)(int))} \]

Writing Function Prototype for 'evaluate'

The function prototype for 'evaluate' lists its return type and parameter signature. Just like the header but includes a semicolon and ends without a body:\[ \text{int evaluate(int x, int (*poly)(int));} \]

Initializing a Character Array

To initialize a character array named 'vowel' with the string of vowels 'AEIOU', you can use two methods. Method 1 uses direct initialization with braces:\[ \text{char vowel[] = "AEIOU";} \]Method 2 uses assignment to individual elements in the array:\[ \begin{align*}\text{char vowel[] = } & \{'A', 'E', 'I', 'O', 'U', '\0'\};\end{align*} \]

Key concepts

Function Headers in C++

A function header in C++ is the part at the beginning of a function definition that tells the compiler about the function's return type, name, and parameter list. Crafting function headers is crucial because it allows other parts of the program to call the function correctly.
In C++, a function header for a function called `exchange` that takes two pointers to double-precision floating-point numbers and doesn't return a value is written as:

• Return Type: `void` indicates the function does not return a value.
• Function Name: The identifier 'exchange'.
• Parameters: Pointers `double* x` and `double* y`, reflecting the function's inputs.

Together, it looks like this: \[\text{void exchange(double* x, double* y)}\].
Function headers can also include qualifiers like `const` or `static`, but in this exercise, we keep it straightforward. They form the blueprint for what inputs a function expects and its output, if any.

Understanding Function Prototypes

Function prototypes in C++ are declarations that inform the compiler about a function's existence and how it can be called before the function's actual definition. They include much of the same information as a function's header, including the return type, function name, and parameter types. However, they end with a semicolon and do not include a function body.
For the 'exchange' function discussed earlier, the prototype is:

• Signature without body: `void exchange(double* x, double* y);`
• Reflects the need for its use before the function is defined later in the code.

Having function prototypes helps the compiler to know functions' characteristics ahead of time and allows for the correct compilation of the code even if function declarations appear after their invocations. This practice not only validates calls to the function but also assists in organizing code efficiently.

Character Arrays and Initialization

Character arrays in C++, often termed char arrays, are sequences of characters stored in contiguous memory locations. They are primarily used to store strings. Initializing character arrays can be done in multiple ways, allowing varied levels of flexibility and control.
For instance, to initialize a character array 'vowel' with the vowels:

• Direct Initialization: \[ \text{char vowel[] = "AEIOU";} \] This method automatically adds a null terminator (\0) to mark the end of the string.
• By elements: \[ \text{char vowel[] = \{'A', 'E', 'I', 'O', 'U', '\0\'};} \] This approach gives explicit control over array termination with the null character.

Each technique has its applications and can be chosen based on the specific needs of the program. Understanding these methods empowers programmers to handle string operations more effectively.

Using Pointer Parameters in Functions

Pointer parameters are a powerful feature in C++ that allow functions to modify variables passed from outside the function body. By using pointers in function parameters, you can pass not just values, but also variable references. This capability is essential in cases where functions need to alter the state or value of the variables being pointed to.
Consider the 'exchange' function, which uses pointer parameters. It swaps the values of two `double` variables.

• The syntax: \[ \text{void exchange(double* x, double* y)} \] showcases the use of pointer parameters, enabling direct access and modification of the referenced variables.
• By manipulating `*x` and `*y`, the function changes the values stored at the addresses pointed to by `x` and `y`.

This approach is highly advantageous when performance is crucial or when working with large data sets, as it eliminates the overhead of copying values. Mastery of pointer parameters can lead to crafting more efficient and dynamic code solutions.