Question

Insert const before any of the following array parameters that can be changed to constant array parameters: void output(double a[], int size); //Precondition: a[0] through a[size - 1] have values. //Postcondition: a[0] through a[size - 1] have been //written out. void drop_odd(int a[], int size); //Precondition: a[0] through a[size - 1] have values. //Postcondition: All odd numbers in a[0] through //a[size - 1] have been changed to 0.

Short answer

Answer: The 'output' function needed the 'const' keyword to be inserted before the 'a[]' parameter because this function only outputs the contents of the array without modifying anything. Adding 'const' ensures that the function does not modify the contents of the input array, preventing unintended behavior.

Step-by-step solution

Function 1: output

For the 'output' function, the input parameters are a double array 'a[]' and an integer 'size'. Since the only purpose of this function is to output the contents of the array without modifying anything, we can make the array parameter 'a[]' constant. The updated function signature should look like this: ```cpp void output(const double a[], int size); ```

Function 2: drop_odd

For the 'drop_odd' function, the input parameters are an integer array 'a[]' and an integer 'size'. This function modifies the contents of the array, specifically changing odd numbers to 0. Because it does modify the array, we cannot make the array parameter 'a[]' constant. Thus, there is no need to add a const keyword in function 2. It should remain as is: ```cpp void drop_odd(int a[], int size); ``` In conclusion, only the 'output' function needed the const keyword to be inserted, ensuring that the function does not modify the contents of the input array.

Key concepts

Understanding the 'const' Keyword

In C++ programming, the `const` keyword is a powerful tool used to indicate immutability. When you declare something as `const`, you're telling both the compiler and the readers of your code that the value will not change. This helps prevent accidental modifications.

Here are some uses of the `const` keyword:

• It can be applied to variables, so their value can't be altered after initial assignment.
• It can be used with pointers to restrict modification of the data pointed to.
• For functions, `const` can guarantee that certain inputs or object states don't change.

Using `const` effectively can make your code safer and easier to understand, reducing bugs caused by unintended changes.

Array Parameters in Functions

In C++, when you pass an array to a function, you're actually passing a pointer to the array's first element. This means that arrays are inherently passed by reference.

Array parameters in functions can often lead to unintended modifications. If you don't want a function to modify the array contents, you can use the `const` keyword.

• This conveys to other programmers that the function won't change the data.
• It helps the compiler enforce this rule, preventing unexpected side-effects.

Ensuring clarity with array parameters is crucial when the intention is only to read data and not change it. This is why making arrays `const` can be vital for maintainable and error-free code.

Defining Function Signatures

A function signature in C++ defines the input and output of a function, which includes the return type, function name, and parameters.

The function signature is crucial as it tells the user what the function does without exposing the inner workings.

• Consists of function name and its parameters.
• Defining parameters as `const` in the signature can convey restrictions around data modification.
• Clear function signatures support seamless code integration and readability.

Crafting a well-defined function signature with `const` parameters when appropriate ensures that a function is clear about what it requires and guarantees certain behaviors.

The Role of Constant Arrays

A constant array in C++ is an array whose contents should not be changed once initialized.

This can be beneficial in situations where you don't want a function to accidentally modify the contents of the array.

• Protects the original data from being altered.
• Ensures that functions reading the array cannot accidentally or purposefully change its contents.
• Increases the trustworthiness of code for use in applications requiring data integrity.

Using constant arrays is a best practice if you need to pass an array to a function purely for reading purposes. This ensures that your data remains secure and predictable throughout.