Problem 5 - C++ How to Program

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".

Step-by-Step Solution

Answer

a) void exchange(double *x, double *y); b) void exchange(double *x, double *y); c) int evaluate(int x, int (*poly)(int)); d) int evaluate(int x, int (*poly)(int)); e) char vowel[] = 'AEIOU'; or using strcpy: char vowel[6]; strcpy(vowel, 'AEIOU');

Step 1: Write the function header for 'exchange'

Start by specifying the keyword 'void' to indicate that the function does not return a value. The function name is 'exchange'. Declare two parameters that are pointers to double-precision floating-point numbers, which are represented as 'double *x' and 'double *y'. The function header will look like this: void exchange(double *x, double *y).

Step 2: Write the function prototype for 'exchange'

The function prototype is identical to the function header but with a semicolon at the end. You should also ensure all necessary include statements or forward declarations are in place for compilation. The prototype will be: void exchange(double *x, double *y);

Step 3: Write the function header for 'evaluate'

The function 'evaluate' must return an integer, so start with 'int' followed by the function name 'evaluate'. Declare the parameters which are an integer 'x' and a pointer to a function named 'poly' that takes an integer parameter and returns an integer. Thus, the parameter type for 'poly' will be a function pointer: int (*poly)(int). The function header will be: int evaluate(int x, int (*poly)(int)).

Step 4: Write the function prototype for 'evaluate'

Like in step 2, the function prototype for 'evaluate' will resemble the header with a semicolon at the end, and ensure you include any necessary details for the pointer to function type. The prototype will be: int evaluate(int x, int (*poly)(int));

Step 5: Initialize character array with vowels

To initialize the character array 'vowel' with the string 'AEIOU', you can use either array initialization or string copy function. Here are two ways you can do this: char vowel[] = 'AEIOU'; (array initialization) or using strcpy: char vowel[6]; strcpy(vowel, 'AEIOU'); (standard library string copy function) Note that in the second method, the array size is 6 to accommodate the null terminator.

Key Concepts

C++ Function Prototypes

In C++, a function prototype, also known as a function declaration, is a statement that provides the compiler with information about the function name, return type, and parameters without the actual function body. It's like giving someone a summary of a book without telling the full story. These are crucial when you have multiple functions that need to know about each other.

For example, the function prototype for the exercise's 'exchange' function is written as void exchange(double *x, double *y);. It tells the compiler that there's a function named 'exchange' which takes two pointers to double-precision numbers as arguments and does not return anything. This allows 'exchange' to be called anywhere in the code after the prototype is declared, enabling better organization and readability of the program.

C++ Function Headers

The function header, often confused with a prototype, is the starting line of the function definition. This is where you roll up your sleeves and get to work on what the function actually does. For instance, the 'exchange' function's header in our exercise is void exchange(double *x, double *y).

Unlike the prototype, the function header leads directly into the body of the function where the implementation details are specified. It must match the prototype declaration in terms of the function name, return type, and parameters. The header is the declaration and the beginning of the actual code that will run when the function is called.

C++ Array Initialization

When it comes to arrays in C++, initializing them properly sets up a smooth ride for your program. Array initialization gives the array its starting values. It's like setting the stage before the actors come out. To initialize an array, you have to specify the values it should hold from the very beginning.

You can initialize an array in C++ using the curly braces syntax. For the character array 'vowel' in our exercise, we can write char vowel[] = 'AEIOU';. This code creates an array with the specific slots filled in with the characters 'A', 'E', 'I', 'O', and 'U'. An important detail is that arrays of characters, called strings in C++, end with a null character to indicate the end of the string, so keep in mind the true size of the array.

C++ Pointer Parameters

Pointers in C++ are like street signs pointing to houses—the houses are the data, and the street signs tell you where the data lives. When you use pointer parameters in functions, you're essentially giving the function the address of the data rather than a copy of the data itself.

Using pointer parameters can be more efficient, since you're not copying large amounts of data around, and it allows the function to modify the original data. For example, in the 'exchange' function from our exercise, the function uses pointer parameters to swap the values of the variables that the pointers are pointing to. The headers show pointer usage with the * symbol, such as in void exchange(double *x, double *y), which signifies that 'x' and 'y' are addresses of double-precision numbers.