Question

Write a function declaration and function definition for a function called read_filter that has no parameters and that returns a value of type double.

Short answer

Answer: The purpose of the read_filter function is to read a double value from the user input and return it without taking any parameters.

Step-by-step solution

Write the function declaration

To declare the function `read_filter`, we need to specify its return type, which is `double`, the name of the function, which is `read_filter`, and an empty parameter list since it takes no parameters. Here is the function declaration: ```cpp double read_filter(); ```

Write the function definition

Now, we need to define the function `read_filter`. We will create a variable of type `double` to store the user-inputted value, and then use `cin` to read the value. Finally, we will return the value that was read. Here is the function definition: ```cpp double read_filter() { double value; std::cout << "Enter a double value: "; std::cin >> value; return value; } ``` To use the `read_filter` function in a program, you would include the function declaration at the beginning (possibly in a header file) and the function definition along with the rest of the code (possibly in a source file). Then, you can call the `read_filter` function, and it will return a double value inputted by the user.